TATurner's AtlasDrill & tube guide

Drill guide/Fractional-inch sizes

Field guide / sizing and fit

Drill-size systems
for pen makers.

A fraction, a letter, a number, and a metric value can describe diameters that are identical, nearly identical, or meaningfully different. Read the kit callout as a specification—not a suggestion—then separate the nominal label from the drill you actually own and the bore your setup actually makes.

Exact conversion
1 in = 25.4 mm
Imperial indexes
Fraction · #80–#1 · A–Z
Fit authority
Current kit instruction
Open drill index with graduated twist drills beside a pen blank, brass tube, and dial caliper
Original Turner's Atlas photo illustration. The case may organize the labels; it cannot tell you what hole your machine will produce.
The short verdict

Convert to compare. Measure to verify. Substitute only with approval.

NIST defines one inch as exactly 25.4 millimetres, so the arithmetic conversion is exact.1 The result is still only a nominal diameter. A nearby metric, number, or letter drill is not automatically interchangeable because the marked sizes differ, individual tools have manufacturing tolerances, and the finished bore includes setup and material effects.

01 / Decode the label

Four systems share one diameter line.

Fractional, number, letter, and metric are naming systems. They do not tell you whether the bit is a brad point, jobber twist, parabolic flute, acrylic grind, or reduced-shank tool.

27/64 inFractional inch

Parts of one inch

Common indexes progress in 1/64-inch steps. The fraction is exact: 27/64 is 0.421875 inch, or 10.715625 mm.

#7Number gauge

#80 small → #1 large

The sequence runs opposite the number: lower drill numbers are larger. The labels are lookup designations, not a formula.3

Letter OLetter gauge

A small → Z large

Letters continue above #1 from A at 0.2340 inch to Z at 0.4130 inch. The letter alone is the size designation.2

10.5 mmMetric

Direct millimetres

The number is already the nominal diameter. Keep it metric instead of rounding to a familiar fraction unless the kit maker lists an alternative.

01Marked size27/64 in
→
02Nominal diameter0.421875 in
→
03Actual drillMaker tolerance + wear
→
04Actual boreRunout + feed + material
→
05Tube fitBore − tube − adhesive

Only the first conversion is pure arithmetic. Every following stage has to be controlled or measured.

02 / Close is not equal

Pen-shop sizes that look interchangeable on paper.

These examples expose the difference directly. “Same nominal” is a dimensional statement; “nearby” is not a fit recommendation.

1/4 in=Letter E
0.0000 in apart

Both designate 0.2500 inch nominal diameter. Tool condition, geometry, and the resulting bore still need verification.

10.5 mm↔Letter Z
0.00039 in · 0.0098 mm

Very close numerically, but not the same nominal size. Do not silently replace one callout with the other.

27/64 in↔10.7 mm
0.00062 in · 0.0156 mm

The fraction converts to 10.715625 mm. A 10.7 mm drill is smaller before tool and process variation enter the stack.

7.0 mm↔Letter J
0.00141 in · 0.0358 mm

Letter J is 0.2770 inch, or 7.0358 mm. That difference changes radial clearance by about 0.0179 mm per side.

3/8 in↔Letter V
0.00200 in · 0.0508 mm

Letter V is larger. The difference may be small to the eye but is significant when tube fit and adhesive film are the goal.

10.5 mm↔27/64 in
0.00849 in · 0.2156 mm

These are plainly different even though both appear frequently in pen-kit instructions. Read which barrel requires which bore.

PSI's own compatibility chart places 7 mm, 8 mm, 3/8 inch, 10 mm, 27/64 inch, 10.5 mm, and .492 inch families in one document.6 That mixture is normal in pen making; rounding them into one system is not.

03 / Search the full reference

A cross-reference—not a substitution chart.

Use the filters to find a marked size or compare two designations. The chart preserves nominal values and reports the difference to the nearest names in the other systems.

Comparison bench

Put two marked sizes side by side.

The result is a nominal diameter comparison—not permission to substitute one drill for another.

vs.
Diameter difference
0.00141 in
0.0358 mm
Radial clearance change
0.00070 in
0.0179 mm per side
Interpretation
Different nominal sizes
Use only if the kit maker approves it.
Master cross-reference

Fractional, number, letter, and metric sizes

Complete #80–#1 and A–Z series, fractional 64ths through 1/2 inch, plus a 0.1–13.0 mm conversion lookup in 0.1 mm steps.

268 rows
Marked sizeSystemDecimal inchMillimetresClosest designation in each other system
0.1 mmMetric lookup0.0039 in0.100 mm
#800.0096 in / 0.243 mm away1/64 in0.0117 in / 0.297 mm awayLetter A0.2301 in / 5.844 mm away
0.2 mmMetric lookup0.0079 in0.200 mm
#800.0056 in / 0.143 mm away1/64 in0.0078 in / 0.197 mm awayLetter A0.2261 in / 5.744 mm away
0.3 mmMetric lookup0.0118 in0.300 mm
#800.0017 in / 0.043 mm away1/64 in0.0038 in / 0.097 mm awayLetter A0.2222 in / 5.644 mm away
#80Number gauge0.0135 in0.343 mm
0.3 mm0.0017 in / 0.043 mm away1/64 in0.0021 in / 0.054 mm awayLetter A0.2205 in / 5.601 mm away
#79Number gauge0.0145 in0.368 mm
1/64 in0.0011 in / 0.029 mm away0.4 mm0.0012 in / 0.032 mm awayLetter A0.2195 in / 5.575 mm away
1/64 inFractional inch0.0156 in0.397 mm
0.4 mm0.0001 in / 0.003 mm away#780.0004 in / 0.010 mm awayLetter A0.2184 in / 5.547 mm away
0.4 mmMetric lookup0.0157 in0.400 mm
1/64 in0.0001 in / 0.003 mm away#780.0003 in / 0.006 mm awayLetter A0.2183 in / 5.544 mm away
#78Number gauge0.0160 in0.406 mm
0.4 mm0.0003 in / 0.006 mm away1/64 in0.0004 in / 0.010 mm awayLetter A0.2180 in / 5.537 mm away
#77Number gauge0.0180 in0.457 mm
0.5 mm0.0017 in / 0.043 mm away1/64 in0.0024 in / 0.060 mm awayLetter A0.2160 in / 5.486 mm away
0.5 mmMetric lookup0.0197 in0.500 mm
#760.0003 in / 0.008 mm away1/64 in0.0041 in / 0.103 mm awayLetter A0.2143 in / 5.444 mm away
#76Number gauge0.0200 in0.508 mm
0.5 mm0.0003 in / 0.008 mm away1/64 in0.0044 in / 0.111 mm awayLetter A0.2140 in / 5.436 mm away
#75Number gauge0.0210 in0.533 mm
0.5 mm0.0013 in / 0.033 mm away1/64 in0.0054 in / 0.137 mm awayLetter A0.2130 in / 5.410 mm away
#74Number gauge0.0225 in0.571 mm
0.6 mm0.0011 in / 0.029 mm away1/64 in0.0069 in / 0.175 mm awayLetter A0.2115 in / 5.372 mm away
0.6 mmMetric lookup0.0236 in0.600 mm
#730.0004 in / 0.010 mm away1/32 in0.0076 in / 0.194 mm awayLetter A0.2104 in / 5.344 mm away
#73Number gauge0.0240 in0.610 mm
0.6 mm0.0004 in / 0.010 mm away1/32 in0.0072 in / 0.184 mm awayLetter A0.2100 in / 5.334 mm away
#72Number gauge0.0250 in0.635 mm
0.6 mm0.0014 in / 0.035 mm away1/32 in0.0062 in / 0.159 mm awayLetter A0.2090 in / 5.309 mm away
#71Number gauge0.0260 in0.660 mm
0.7 mm0.0016 in / 0.040 mm away1/32 in0.0053 in / 0.133 mm awayLetter A0.2080 in / 5.283 mm away
0.7 mmMetric lookup0.0276 in0.700 mm
#700.0004 in / 0.011 mm away1/32 in0.0037 in / 0.094 mm awayLetter A0.2064 in / 5.244 mm away
#70Number gauge0.0280 in0.711 mm
0.7 mm0.0004 in / 0.011 mm away1/32 in0.0032 in / 0.083 mm awayLetter A0.2060 in / 5.232 mm away
#69Number gauge0.0292 in0.742 mm
0.7 mm0.0016 in / 0.042 mm away1/32 in0.0020 in / 0.052 mm awayLetter A0.2048 in / 5.202 mm away
#68Number gauge0.0310 in0.787 mm
1/32 in0.0003 in / 0.006 mm away0.8 mm0.0005 in / 0.013 mm awayLetter A0.2030 in / 5.156 mm away
1/32 inFractional inch0.0313 in0.794 mm
0.8 mm0.0002 in / 0.006 mm away#680.0003 in / 0.006 mm awayLetter A0.2028 in / 5.150 mm away
0.8 mmMetric lookup0.0315 in0.800 mm
1/32 in0.0002 in / 0.006 mm away#680.0005 in / 0.013 mm awayLetter A0.2025 in / 5.144 mm away
#67Number gauge0.0320 in0.813 mm
0.8 mm0.0005 in / 0.013 mm away1/32 in0.0008 in / 0.019 mm awayLetter A0.2020 in / 5.131 mm away
#66Number gauge0.0330 in0.838 mm
0.8 mm0.0015 in / 0.038 mm away1/32 in0.0018 in / 0.044 mm awayLetter A0.2010 in / 5.105 mm away
#65Number gauge0.0350 in0.889 mm
0.9 mm0.0004 in / 0.011 mm away1/32 in0.0038 in / 0.095 mm awayLetter A0.1990 in / 5.055 mm away
0.9 mmMetric lookup0.0354 in0.900 mm
#650.0004 in / 0.011 mm away1/32 in0.0042 in / 0.106 mm awayLetter A0.1986 in / 5.044 mm away
#64Number gauge0.0360 in0.914 mm
0.9 mm0.0006 in / 0.014 mm away1/32 in0.0047 in / 0.121 mm awayLetter A0.1980 in / 5.029 mm away
#63Number gauge0.0370 in0.940 mm
0.9 mm0.0016 in / 0.040 mm away1/32 in0.0057 in / 0.146 mm awayLetter A0.1970 in / 5.004 mm away
#62Number gauge0.0380 in0.965 mm
1.0 mm0.0014 in / 0.035 mm away1/32 in0.0067 in / 0.171 mm awayLetter A0.1960 in / 4.978 mm away
#61Number gauge0.0390 in0.991 mm
1.0 mm0.0004 in / 0.009 mm away1/32 in0.0077 in / 0.197 mm awayLetter A0.1950 in / 4.953 mm away
1.0 mmMetric lookup0.0394 in1.000 mm
#610.0004 in / 0.009 mm away3/64 in0.0075 in / 0.191 mm awayLetter A0.1946 in / 4.944 mm away
#60Number gauge0.0400 in1.016 mm
1.0 mm0.0006 in / 0.016 mm away3/64 in0.0069 in / 0.175 mm awayLetter A0.1940 in / 4.928 mm away
#59Number gauge0.0410 in1.041 mm
1.0 mm0.0016 in / 0.041 mm away3/64 in0.0059 in / 0.149 mm awayLetter A0.1930 in / 4.902 mm away
#58Number gauge0.0420 in1.067 mm
1.1 mm0.0013 in / 0.033 mm away3/64 in0.0049 in / 0.124 mm awayLetter A0.1920 in / 4.877 mm away
#57Number gauge0.0430 in1.092 mm
1.1 mm0.0003 in / 0.008 mm away3/64 in0.0039 in / 0.098 mm awayLetter A0.1910 in / 4.851 mm away
1.1 mmMetric lookup0.0433 in1.100 mm
#570.0003 in / 0.008 mm away3/64 in0.0036 in / 0.091 mm awayLetter A0.1907 in / 4.844 mm away
#56Number gauge0.0465 in1.181 mm
3/64 in0.0004 in / 0.010 mm away1.2 mm0.0007 in / 0.019 mm awayLetter A0.1875 in / 4.762 mm away
3/64 inFractional inch0.0469 in1.191 mm
1.2 mm0.0004 in / 0.009 mm away#560.0004 in / 0.010 mm awayLetter A0.1871 in / 4.753 mm away
1.2 mmMetric lookup0.0472 in1.200 mm
3/64 in0.0004 in / 0.009 mm away#560.0007 in / 0.019 mm awayLetter A0.1868 in / 4.744 mm away
1.3 mmMetric lookup0.0512 in1.300 mm
#550.0008 in / 0.021 mm away3/64 in0.0043 in / 0.109 mm awayLetter A0.1828 in / 4.644 mm away
#55Number gauge0.0520 in1.321 mm
1.3 mm0.0008 in / 0.021 mm away3/64 in0.0051 in / 0.130 mm awayLetter A0.1820 in / 4.623 mm away
#54Number gauge0.0550 in1.397 mm
1.4 mm0.0001 in / 0.003 mm away1/16 in0.0075 in / 0.190 mm awayLetter A0.1790 in / 4.547 mm away
1.4 mmMetric lookup0.0551 in1.400 mm
#540.0001 in / 0.003 mm away1/16 in0.0074 in / 0.188 mm awayLetter A0.1789 in / 4.544 mm away
1.5 mmMetric lookup0.0591 in1.500 mm
#530.0004 in / 0.011 mm away1/16 in0.0034 in / 0.087 mm awayLetter A0.1749 in / 4.444 mm away
#53Number gauge0.0595 in1.511 mm
1.5 mm0.0004 in / 0.011 mm away1/16 in0.0030 in / 0.076 mm awayLetter A0.1745 in / 4.432 mm away
1/16 inFractional inch0.0625 in1.587 mm
1.6 mm0.0005 in / 0.013 mm away#520.0010 in / 0.025 mm awayLetter A0.1715 in / 4.356 mm away
1.6 mmMetric lookup0.0630 in1.600 mm
1/16 in0.0005 in / 0.013 mm away#520.0005 in / 0.013 mm awayLetter A0.1710 in / 4.344 mm away
#52Number gauge0.0635 in1.613 mm
1.6 mm0.0005 in / 0.013 mm away1/16 in0.0010 in / 0.025 mm awayLetter A0.1705 in / 4.331 mm away
1.7 mmMetric lookup0.0669 in1.700 mm
#510.0001 in / 0.002 mm away1/16 in0.0044 in / 0.113 mm awayLetter A0.1671 in / 4.244 mm away
#51Number gauge0.0670 in1.702 mm
1.7 mm0.0001 in / 0.002 mm away1/16 in0.0045 in / 0.114 mm awayLetter A0.1670 in / 4.242 mm away
#50Number gauge0.0700 in1.778 mm
1.8 mm0.0009 in / 0.022 mm away1/16 in0.0075 in / 0.191 mm awayLetter A0.1640 in / 4.166 mm away
1.8 mmMetric lookup0.0709 in1.800 mm
#500.0009 in / 0.022 mm away5/64 in0.0073 in / 0.184 mm awayLetter A0.1631 in / 4.144 mm away
#49Number gauge0.0730 in1.854 mm
1.9 mm0.0018 in / 0.046 mm away5/64 in0.0051 in / 0.130 mm awayLetter A0.1610 in / 4.089 mm away
1.9 mmMetric lookup0.0748 in1.900 mm
#480.0012 in / 0.030 mm away5/64 in0.0033 in / 0.084 mm awayLetter A0.1592 in / 4.044 mm away
#48Number gauge0.0760 in1.930 mm
1.9 mm0.0012 in / 0.030 mm away5/64 in0.0021 in / 0.054 mm awayLetter A0.1580 in / 4.013 mm away
5/64 inFractional inch0.0781 in1.984 mm
#470.0004 in / 0.010 mm away2.0 mm0.0006 in / 0.016 mm awayLetter A0.1559 in / 3.959 mm away
#47Number gauge0.0785 in1.994 mm
2.0 mm0.0002 in / 0.006 mm away5/64 in0.0004 in / 0.010 mm awayLetter A0.1555 in / 3.950 mm away
2.0 mmMetric lookup0.0787 in2.000 mm
#470.0002 in / 0.006 mm away5/64 in0.0006 in / 0.016 mm awayLetter A0.1553 in / 3.944 mm away
#46Number gauge0.0810 in2.057 mm
2.1 mm0.0017 in / 0.043 mm away5/64 in0.0029 in / 0.073 mm awayLetter A0.1530 in / 3.886 mm away
#45Number gauge0.0820 in2.083 mm
2.1 mm0.0007 in / 0.017 mm away5/64 in0.0039 in / 0.098 mm awayLetter A0.1520 in / 3.861 mm away
2.1 mmMetric lookup0.0827 in2.100 mm
#450.0007 in / 0.017 mm away5/64 in0.0046 in / 0.116 mm awayLetter A0.1513 in / 3.844 mm away
#44Number gauge0.0860 in2.184 mm
2.2 mm0.0006 in / 0.016 mm away3/32 in0.0078 in / 0.197 mm awayLetter A0.1480 in / 3.759 mm away
2.2 mmMetric lookup0.0866 in2.200 mm
#440.0006 in / 0.016 mm away3/32 in0.0071 in / 0.181 mm awayLetter A0.1474 in / 3.744 mm away
#43Number gauge0.0890 in2.261 mm
2.3 mm0.0016 in / 0.039 mm away3/32 in0.0048 in / 0.121 mm awayLetter A0.1450 in / 3.683 mm away
2.3 mmMetric lookup0.0906 in2.300 mm
#430.0016 in / 0.039 mm away3/32 in0.0032 in / 0.081 mm awayLetter A0.1434 in / 3.644 mm away
#42Number gauge0.0935 in2.375 mm
3/32 in0.0003 in / 0.006 mm away2.4 mm0.0010 in / 0.025 mm awayLetter A0.1405 in / 3.569 mm away
3/32 inFractional inch0.0938 in2.381 mm
#420.0003 in / 0.006 mm away2.4 mm0.0007 in / 0.019 mm awayLetter A0.1403 in / 3.562 mm away
2.4 mmMetric lookup0.0945 in2.400 mm
3/32 in0.0007 in / 0.019 mm away#420.0010 in / 0.025 mm awayLetter A0.1395 in / 3.544 mm away
#41Number gauge0.0960 in2.438 mm
2.4 mm0.0015 in / 0.038 mm away3/32 in0.0023 in / 0.057 mm awayLetter A0.1380 in / 3.505 mm away
#40Number gauge0.0980 in2.489 mm
2.5 mm0.0004 in / 0.011 mm away3/32 in0.0043 in / 0.108 mm awayLetter A0.1360 in / 3.454 mm away
2.5 mmMetric lookup0.0984 in2.500 mm
#400.0004 in / 0.011 mm away3/32 in0.0047 in / 0.119 mm awayLetter A0.1356 in / 3.444 mm away
#39Number gauge0.0995 in2.527 mm
2.5 mm0.0011 in / 0.027 mm away3/32 in0.0058 in / 0.146 mm awayLetter A0.1345 in / 3.416 mm away
#38Number gauge0.1015 in2.578 mm
2.6 mm0.0009 in / 0.022 mm away3/32 in0.0078 in / 0.197 mm awayLetter A0.1325 in / 3.365 mm away
2.6 mmMetric lookup0.1024 in2.600 mm
#380.0009 in / 0.022 mm away7/64 in0.0070 in / 0.178 mm awayLetter A0.1316 in / 3.344 mm away
#37Number gauge0.1040 in2.642 mm
2.6 mm0.0016 in / 0.042 mm away7/64 in0.0054 in / 0.137 mm awayLetter A0.1300 in / 3.302 mm away
2.7 mmMetric lookup0.1063 in2.700 mm
#360.0002 in / 0.005 mm away7/64 in0.0031 in / 0.078 mm awayLetter A0.1277 in / 3.244 mm away
#36Number gauge0.1065 in2.705 mm
2.7 mm0.0002 in / 0.005 mm away7/64 in0.0029 in / 0.073 mm awayLetter A0.1275 in / 3.238 mm away
7/64 inFractional inch0.1094 in2.778 mm
#350.0006 in / 0.016 mm away2.8 mm0.0009 in / 0.022 mm awayLetter A0.1246 in / 3.165 mm away
#35Number gauge0.1100 in2.794 mm
2.8 mm0.0002 in / 0.006 mm away7/64 in0.0006 in / 0.016 mm awayLetter A0.1240 in / 3.150 mm away
2.8 mmMetric lookup0.1102 in2.800 mm
#350.0002 in / 0.006 mm away7/64 in0.0009 in / 0.022 mm awayLetter A0.1238 in / 3.144 mm away
#34Number gauge0.1110 in2.819 mm
2.8 mm0.0008 in / 0.019 mm away7/64 in0.0016 in / 0.041 mm awayLetter A0.1230 in / 3.124 mm away
#33Number gauge0.1130 in2.870 mm
2.9 mm0.0012 in / 0.030 mm away7/64 in0.0036 in / 0.092 mm awayLetter A0.1210 in / 3.073 mm away
2.9 mmMetric lookup0.1142 in2.900 mm
#330.0012 in / 0.030 mm away7/64 in0.0048 in / 0.122 mm awayLetter A0.1198 in / 3.044 mm away
#32Number gauge0.1160 in2.946 mm
2.9 mm0.0018 in / 0.046 mm away7/64 in0.0066 in / 0.168 mm awayLetter A0.1180 in / 2.997 mm away
3.0 mmMetric lookup0.1181 in3.000 mm
#310.0019 in / 0.048 mm away1/8 in0.0069 in / 0.175 mm awayLetter A0.1159 in / 2.944 mm away
#31Number gauge0.1200 in3.048 mm
3.0 mm0.0019 in / 0.048 mm away1/8 in0.0050 in / 0.127 mm awayLetter A0.1140 in / 2.896 mm away
3.1 mmMetric lookup0.1220 in3.100 mm
#310.0020 in / 0.052 mm away1/8 in0.0030 in / 0.075 mm awayLetter A0.1120 in / 2.844 mm away
1/8 inFractional inch0.1250 in3.175 mm
3.2 mm0.0010 in / 0.025 mm away#300.0035 in / 0.089 mm awayLetter A0.1090 in / 2.769 mm away
3.2 mmMetric lookup0.1260 in3.200 mm
1/8 in0.0010 in / 0.025 mm away#300.0025 in / 0.064 mm awayLetter A0.1080 in / 2.744 mm away
#30Number gauge0.1285 in3.264 mm
3.3 mm0.0014 in / 0.036 mm away1/8 in0.0035 in / 0.089 mm awayLetter A0.1055 in / 2.680 mm away
3.3 mmMetric lookup0.1299 in3.300 mm
#300.0014 in / 0.036 mm away1/8 in0.0049 in / 0.125 mm awayLetter A0.1041 in / 2.644 mm away
3.4 mmMetric lookup0.1339 in3.400 mm
#290.0021 in / 0.054 mm away9/64 in0.0068 in / 0.172 mm awayLetter A0.1001 in / 2.544 mm away
#29Number gauge0.1360 in3.454 mm
3.5 mm0.0018 in / 0.046 mm away9/64 in0.0046 in / 0.117 mm awayLetter A0.0980 in / 2.489 mm away
3.5 mmMetric lookup0.1378 in3.500 mm
#290.0018 in / 0.046 mm away9/64 in0.0028 in / 0.072 mm awayLetter A0.0962 in / 2.444 mm away
#28Number gauge0.1405 in3.569 mm
9/64 in0.0001 in / 0.003 mm away3.6 mm0.0012 in / 0.031 mm awayLetter A0.0935 in / 2.375 mm away
9/64 inFractional inch0.1406 in3.572 mm
#280.0001 in / 0.003 mm away3.6 mm0.0011 in / 0.028 mm awayLetter A0.0934 in / 2.372 mm away
3.6 mmMetric lookup0.1417 in3.600 mm
9/64 in0.0011 in / 0.028 mm away#280.0012 in / 0.031 mm awayLetter A0.0923 in / 2.344 mm away
#27Number gauge0.1440 in3.658 mm
3.7 mm0.0017 in / 0.042 mm away9/64 in0.0034 in / 0.086 mm awayLetter A0.0900 in / 2.286 mm away
3.7 mmMetric lookup0.1457 in3.700 mm
#260.0013 in / 0.034 mm away9/64 in0.0050 in / 0.128 mm awayLetter A0.0883 in / 2.244 mm away
#26Number gauge0.1470 in3.734 mm
3.7 mm0.0013 in / 0.034 mm away9/64 in0.0064 in / 0.162 mm awayLetter A0.0870 in / 2.210 mm away
#25Number gauge0.1495 in3.797 mm
3.8 mm0.0001 in / 0.003 mm away5/32 in0.0068 in / 0.171 mm awayLetter A0.0845 in / 2.146 mm away
3.8 mmMetric lookup0.1496 in3.800 mm
#250.0001 in / 0.003 mm away5/32 in0.0066 in / 0.169 mm awayLetter A0.0844 in / 2.144 mm away
#24Number gauge0.1520 in3.861 mm
3.9 mm0.0015 in / 0.039 mm away5/32 in0.0043 in / 0.108 mm awayLetter A0.0820 in / 2.083 mm away
3.9 mmMetric lookup0.1535 in3.900 mm
#230.0005 in / 0.012 mm away5/32 in0.0027 in / 0.069 mm awayLetter A0.0805 in / 2.044 mm away
#23Number gauge0.1540 in3.912 mm
3.9 mm0.0005 in / 0.012 mm away5/32 in0.0023 in / 0.057 mm awayLetter A0.0800 in / 2.032 mm away
5/32 inFractional inch0.1563 in3.969 mm
#220.0008 in / 0.019 mm away4.0 mm0.0012 in / 0.031 mm awayLetter A0.0778 in / 1.975 mm away
#22Number gauge0.1570 in3.988 mm
4.0 mm0.0005 in / 0.012 mm away5/32 in0.0008 in / 0.019 mm awayLetter A0.0770 in / 1.956 mm away
4.0 mmMetric lookup0.1575 in4.000 mm
#220.0005 in / 0.012 mm away5/32 in0.0012 in / 0.031 mm awayLetter A0.0765 in / 1.944 mm away
#21Number gauge0.1590 in4.039 mm
4.0 mm0.0015 in / 0.039 mm away5/32 in0.0028 in / 0.070 mm awayLetter A0.0750 in / 1.905 mm away
#20Number gauge0.1610 in4.089 mm
4.1 mm0.0004 in / 0.011 mm away5/32 in0.0048 in / 0.121 mm awayLetter A0.0730 in / 1.854 mm away
4.1 mmMetric lookup0.1614 in4.100 mm
#200.0004 in / 0.011 mm away5/32 in0.0052 in / 0.131 mm awayLetter A0.0726 in / 1.844 mm away
4.2 mmMetric lookup0.1654 in4.200 mm
#190.0006 in / 0.016 mm away11/64 in0.0065 in / 0.166 mm awayLetter A0.0686 in / 1.744 mm away
#19Number gauge0.1660 in4.216 mm
4.2 mm0.0006 in / 0.016 mm away11/64 in0.0059 in / 0.149 mm awayLetter A0.0680 in / 1.727 mm away
4.3 mmMetric lookup0.1693 in4.300 mm
#180.0002 in / 0.005 mm away11/64 in0.0026 in / 0.066 mm awayLetter A0.0647 in / 1.644 mm away
#18Number gauge0.1695 in4.305 mm
4.3 mm0.0002 in / 0.005 mm away11/64 in0.0024 in / 0.060 mm awayLetter A0.0645 in / 1.638 mm away
11/64 inFractional inch0.1719 in4.366 mm
#170.0011 in / 0.029 mm away4.4 mm0.0014 in / 0.034 mm awayLetter A0.0621 in / 1.578 mm away
#17Number gauge0.1730 in4.394 mm
4.4 mm0.0002 in / 0.006 mm away11/64 in0.0011 in / 0.029 mm awayLetter A0.0610 in / 1.549 mm away
4.4 mmMetric lookup0.1732 in4.400 mm
#170.0002 in / 0.006 mm away11/64 in0.0014 in / 0.034 mm awayLetter A0.0608 in / 1.544 mm away
#16Number gauge0.1770 in4.496 mm
4.5 mm0.0002 in / 0.004 mm away11/64 in0.0051 in / 0.130 mm awayLetter A0.0570 in / 1.448 mm away
4.5 mmMetric lookup0.1772 in4.500 mm
#160.0002 in / 0.004 mm away11/64 in0.0053 in / 0.134 mm awayLetter A0.0568 in / 1.444 mm away
#15Number gauge0.1800 in4.572 mm
4.6 mm0.0011 in / 0.028 mm away3/16 in0.0075 in / 0.191 mm awayLetter A0.0540 in / 1.372 mm away
4.6 mmMetric lookup0.1811 in4.600 mm
#140.0009 in / 0.023 mm away3/16 in0.0064 in / 0.163 mm awayLetter A0.0529 in / 1.344 mm away
#14Number gauge0.1820 in4.623 mm
4.6 mm0.0009 in / 0.023 mm away3/16 in0.0055 in / 0.140 mm awayLetter A0.0520 in / 1.321 mm away
#13Number gauge0.1850 in4.699 mm
4.7 mm0.0000 in / 0.001 mm away3/16 in0.0025 in / 0.064 mm awayLetter A0.0490 in / 1.245 mm away
4.7 mmMetric lookup0.1850 in4.700 mm
#130.0000 in / 0.001 mm away3/16 in0.0025 in / 0.062 mm awayLetter A0.0490 in / 1.244 mm away
3/16 inFractional inch0.1875 in4.762 mm
4.8 mm0.0015 in / 0.037 mm away#120.0015 in / 0.038 mm awayLetter A0.0465 in / 1.181 mm away
4.8 mmMetric lookup0.1890 in4.800 mm
#120.0000 in / 0.001 mm away3/16 in0.0015 in / 0.037 mm awayLetter A0.0450 in / 1.144 mm away
#12Number gauge0.1890 in4.801 mm
4.8 mm0.0000 in / 0.001 mm away3/16 in0.0015 in / 0.038 mm awayLetter A0.0450 in / 1.143 mm away
#11Number gauge0.1910 in4.851 mm
4.9 mm0.0019 in / 0.049 mm away3/16 in0.0035 in / 0.089 mm awayLetter A0.0430 in / 1.092 mm away
4.9 mmMetric lookup0.1929 in4.900 mm
#100.0006 in / 0.015 mm away3/16 in0.0054 in / 0.138 mm awayLetter A0.0411 in / 1.044 mm away
#10Number gauge0.1935 in4.915 mm
4.9 mm0.0006 in / 0.015 mm away3/16 in0.0060 in / 0.152 mm awayLetter A0.0405 in / 1.029 mm away
#9Number gauge0.1960 in4.978 mm
5.0 mm0.0009 in / 0.022 mm away13/64 in0.0071 in / 0.181 mm awayLetter A0.0380 in / 0.965 mm away
5.0 mmMetric lookup0.1969 in5.000 mm
#90.0009 in / 0.022 mm away13/64 in0.0063 in / 0.159 mm awayLetter A0.0371 in / 0.944 mm away
#8Number gauge0.1990 in5.055 mm
5.1 mm0.0018 in / 0.045 mm away13/64 in0.0041 in / 0.105 mm awayLetter A0.0350 in / 0.889 mm away
5.1 mmMetric lookup0.2008 in5.100 mm
#70.0002 in / 0.005 mm away13/64 in0.0023 in / 0.059 mm awayLetter A0.0332 in / 0.844 mm away
#7Number gauge0.2010 in5.105 mm
5.1 mm0.0002 in / 0.005 mm away13/64 in0.0021 in / 0.054 mm awayLetter A0.0330 in / 0.838 mm away
13/64 inFractional inch0.2031 in5.159 mm
#60.0009 in / 0.022 mm away5.2 mm0.0016 in / 0.041 mm awayLetter A0.0309 in / 0.784 mm away
#6Number gauge0.2040 in5.182 mm
5.2 mm0.0007 in / 0.018 mm away13/64 in0.0009 in / 0.022 mm awayLetter A0.0300 in / 0.762 mm away
5.2 mmMetric lookup0.2047 in5.200 mm
#60.0007 in / 0.018 mm away13/64 in0.0016 in / 0.041 mm awayLetter A0.0293 in / 0.744 mm away
#5Number gauge0.2055 in5.220 mm
5.2 mm0.0008 in / 0.020 mm away13/64 in0.0024 in / 0.060 mm awayLetter A0.0285 in / 0.724 mm away
5.3 mmMetric lookup0.2087 in5.300 mm
#40.0003 in / 0.009 mm away13/64 in0.0055 in / 0.141 mm awayLetter A0.0253 in / 0.644 mm away
#4Number gauge0.2090 in5.309 mm
5.3 mm0.0003 in / 0.009 mm away13/64 in0.0059 in / 0.149 mm awayLetter A0.0250 in / 0.635 mm away
5.4 mmMetric lookup0.2126 in5.400 mm
#30.0004 in / 0.010 mm away7/32 in0.0062 in / 0.156 mm awayLetter A0.0214 in / 0.544 mm away
#3Number gauge0.2130 in5.410 mm
5.4 mm0.0004 in / 0.010 mm away7/32 in0.0058 in / 0.146 mm awayLetter A0.0210 in / 0.533 mm away
5.5 mmMetric lookup0.2165 in5.500 mm
7/32 in0.0022 in / 0.056 mm away#30.0035 in / 0.090 mm awayLetter A0.0175 in / 0.444 mm away
7/32 inFractional inch0.2188 in5.556 mm
5.6 mm0.0017 in / 0.044 mm away#20.0023 in / 0.057 mm awayLetter A0.0153 in / 0.387 mm away
5.6 mmMetric lookup0.2205 in5.600 mm
#20.0005 in / 0.013 mm away7/32 in0.0017 in / 0.044 mm awayLetter A0.0135 in / 0.344 mm away
#2Number gauge0.2210 in5.613 mm
5.6 mm0.0005 in / 0.013 mm away7/32 in0.0023 in / 0.057 mm awayLetter A0.0130 in / 0.330 mm away
5.7 mmMetric lookup0.2244 in5.700 mm
#20.0034 in / 0.087 mm away7/32 in0.0057 in / 0.144 mm awayLetter A0.0096 in / 0.244 mm away
#1Number gauge0.2280 in5.791 mm
5.8 mm0.0003 in / 0.009 mm awayLetter A0.0060 in / 0.152 mm away15/64 in0.0064 in / 0.162 mm away
5.8 mmMetric lookup0.2283 in5.800 mm
#10.0003 in / 0.009 mm awayLetter A0.0057 in / 0.144 mm away15/64 in0.0060 in / 0.153 mm away
5.9 mmMetric lookup0.2323 in5.900 mm
Letter A0.0017 in / 0.044 mm away15/64 in0.0021 in / 0.053 mm away#10.0043 in / 0.109 mm away
Letter ALetter gauge0.2340 in5.944 mm
15/64 in0.0004 in / 0.010 mm away5.9 mm0.0017 in / 0.044 mm away#10.0060 in / 0.152 mm away
15/64 inFractional inch0.2344 in5.953 mm
Letter A0.0004 in / 0.010 mm away6.0 mm0.0018 in / 0.047 mm away#10.0064 in / 0.162 mm away
6.0 mmMetric lookup0.2362 in6.000 mm
Letter B0.0018 in / 0.045 mm away15/64 in0.0018 in / 0.047 mm away#10.0082 in / 0.209 mm away
Letter BLetter gauge0.2380 in6.045 mm
6.0 mm0.0018 in / 0.045 mm away15/64 in0.0036 in / 0.092 mm away#10.0100 in / 0.254 mm away
6.1 mmMetric lookup0.2402 in6.100 mm
Letter C0.0018 in / 0.047 mm away15/64 in0.0058 in / 0.147 mm away#10.0122 in / 0.309 mm away
Letter CLetter gauge0.2420 in6.147 mm
6.1 mm0.0018 in / 0.047 mm away15/64 in0.0076 in / 0.194 mm away#10.0140 in / 0.356 mm away
6.2 mmMetric lookup0.2441 in6.200 mm
Letter D0.0019 in / 0.048 mm away1/4 in0.0059 in / 0.150 mm away#10.0161 in / 0.409 mm away
Letter DLetter gauge0.2460 in6.248 mm
6.2 mm0.0019 in / 0.048 mm away1/4 in0.0040 in / 0.102 mm away#10.0180 in / 0.457 mm away
6.3 mmMetric lookup0.2480 in6.300 mm
1/4 in0.0020 in / 0.050 mm awayLetter E0.0020 in / 0.050 mm away#10.0200 in / 0.509 mm away
1/4 inFractional inch0.2500 in6.350 mm
Letter Esame nominal diameter6.3 mm0.0020 in / 0.050 mm away#10.0220 in / 0.559 mm away
Letter ELetter gauge0.2500 in6.350 mm
1/4 insame nominal diameter6.3 mm0.0020 in / 0.050 mm away#10.0220 in / 0.559 mm away
6.4 mmMetric lookup0.2520 in6.400 mm
1/4 in0.0020 in / 0.050 mm awayLetter E0.0020 in / 0.050 mm away#10.0240 in / 0.609 mm away
6.5 mmMetric lookup0.2559 in6.500 mm
Letter F0.0011 in / 0.028 mm away1/4 in0.0059 in / 0.150 mm away#10.0279 in / 0.709 mm away
Letter FLetter gauge0.2570 in6.528 mm
6.5 mm0.0011 in / 0.028 mm away1/4 in0.0070 in / 0.178 mm away#10.0290 in / 0.737 mm away
6.6 mmMetric lookup0.2598 in6.600 mm
Letter G0.0012 in / 0.029 mm away17/64 in0.0058 in / 0.147 mm away#10.0318 in / 0.809 mm away
Letter GLetter gauge0.2610 in6.629 mm
6.6 mm0.0012 in / 0.029 mm away17/64 in0.0046 in / 0.117 mm away#10.0330 in / 0.838 mm away
6.7 mmMetric lookup0.2638 in6.700 mm
17/64 in0.0018 in / 0.047 mm awayLetter H0.0022 in / 0.056 mm away#10.0358 in / 0.909 mm away
17/64 inFractional inch0.2656 in6.747 mm
Letter H0.0004 in / 0.010 mm away6.7 mm0.0018 in / 0.047 mm away#10.0376 in / 0.956 mm away
Letter HLetter gauge0.2660 in6.756 mm
17/64 in0.0004 in / 0.010 mm away6.8 mm0.0017 in / 0.044 mm away#10.0380 in / 0.965 mm away
6.8 mmMetric lookup0.2677 in6.800 mm
Letter H0.0017 in / 0.044 mm away17/64 in0.0021 in / 0.053 mm away#10.0397 in / 1.009 mm away
6.9 mmMetric lookup0.2717 in6.900 mm
Letter I0.0003 in / 0.009 mm away17/64 in0.0060 in / 0.153 mm away#10.0437 in / 1.109 mm away
Letter ILetter gauge0.2720 in6.909 mm
6.9 mm0.0003 in / 0.009 mm away17/64 in0.0064 in / 0.162 mm away#10.0440 in / 1.118 mm away
7.0 mmMetric lookup0.2756 in7.000 mm
Letter J0.0014 in / 0.036 mm away9/32 in0.0057 in / 0.144 mm away#10.0476 in / 1.209 mm away
Letter JLetter gauge0.2770 in7.036 mm
7.0 mm0.0014 in / 0.036 mm away9/32 in0.0042 in / 0.108 mm away#10.0490 in / 1.245 mm away
7.1 mmMetric lookup0.2795 in7.100 mm
Letter K0.0015 in / 0.037 mm away9/32 in0.0017 in / 0.044 mm away#10.0515 in / 1.309 mm away
Letter KLetter gauge0.2810 in7.137 mm
9/32 in0.0002 in / 0.006 mm away7.1 mm0.0015 in / 0.037 mm away#10.0530 in / 1.346 mm away
9/32 inFractional inch0.2813 in7.144 mm
Letter K0.0002 in / 0.006 mm away7.1 mm0.0017 in / 0.044 mm away#10.0532 in / 1.353 mm away
7.2 mmMetric lookup0.2835 in7.200 mm
9/32 in0.0022 in / 0.056 mm awayLetter K0.0025 in / 0.063 mm away#10.0555 in / 1.409 mm away
7.3 mmMetric lookup0.2874 in7.300 mm
Letter L0.0026 in / 0.066 mm away9/32 in0.0062 in / 0.156 mm away#10.0594 in / 1.509 mm away
Letter LLetter gauge0.2900 in7.366 mm
7.4 mm0.0013 in / 0.034 mm away19/64 in0.0069 in / 0.175 mm away#10.0620 in / 1.575 mm away
7.4 mmMetric lookup0.2913 in7.400 mm
Letter L0.0013 in / 0.034 mm away19/64 in0.0055 in / 0.141 mm away#10.0633 in / 1.609 mm away
Letter MLetter gauge0.2950 in7.493 mm
7.5 mm0.0003 in / 0.007 mm away19/64 in0.0019 in / 0.048 mm away#10.0670 in / 1.702 mm away
7.5 mmMetric lookup0.2953 in7.500 mm
Letter M0.0003 in / 0.007 mm away19/64 in0.0016 in / 0.041 mm away#10.0673 in / 1.709 mm away
19/64 inFractional inch0.2969 in7.541 mm
7.5 mm0.0016 in / 0.041 mm awayLetter M0.0019 in / 0.048 mm away#10.0689 in / 1.749 mm away
7.6 mmMetric lookup0.2992 in7.600 mm
19/64 in0.0023 in / 0.059 mm awayLetter N0.0028 in / 0.071 mm away#10.0712 in / 1.809 mm away
Letter NLetter gauge0.3020 in7.671 mm
7.7 mm0.0011 in / 0.029 mm away19/64 in0.0051 in / 0.130 mm away#10.0740 in / 1.880 mm away
7.7 mmMetric lookup0.3031 in7.700 mm
Letter N0.0011 in / 0.029 mm away19/64 in0.0063 in / 0.159 mm away#10.0751 in / 1.909 mm away
7.8 mmMetric lookup0.3071 in7.800 mm
Letter N0.0051 in / 0.129 mm away5/16 in0.0054 in / 0.137 mm away#10.0791 in / 2.009 mm away
7.9 mmMetric lookup0.3110 in7.900 mm
5/16 in0.0015 in / 0.037 mm awayLetter O0.0050 in / 0.126 mm away#10.0830 in / 2.109 mm away
5/16 inFractional inch0.3125 in7.938 mm
7.9 mm0.0015 in / 0.037 mm awayLetter O0.0035 in / 0.089 mm away#10.0845 in / 2.146 mm away
8.0 mmMetric lookup0.3150 in8.000 mm
Letter O0.0010 in / 0.026 mm away5/16 in0.0025 in / 0.062 mm away#10.0870 in / 2.209 mm away
Letter OLetter gauge0.3160 in8.026 mm
8.0 mm0.0010 in / 0.026 mm away5/16 in0.0035 in / 0.089 mm away#10.0880 in / 2.235 mm away
8.1 mmMetric lookup0.3189 in8.100 mm
Letter O0.0029 in / 0.074 mm away5/16 in0.0064 in / 0.162 mm away#10.0909 in / 2.309 mm away
8.2 mmMetric lookup0.3228 in8.200 mm
Letter P0.0002 in / 0.004 mm away21/64 in0.0053 in / 0.134 mm away#10.0948 in / 2.409 mm away
Letter PLetter gauge0.3230 in8.204 mm
8.2 mm0.0002 in / 0.004 mm away21/64 in0.0051 in / 0.130 mm away#10.0950 in / 2.413 mm away
8.3 mmMetric lookup0.3268 in8.300 mm
21/64 in0.0014 in / 0.034 mm awayLetter P0.0038 in / 0.096 mm away#10.0988 in / 2.509 mm away
21/64 inFractional inch0.3281 in8.334 mm
8.3 mm0.0014 in / 0.034 mm awayLetter Q0.0039 in / 0.098 mm away#10.1001 in / 2.543 mm away
8.4 mmMetric lookup0.3307 in8.400 mm
Letter Q0.0013 in / 0.033 mm away21/64 in0.0026 in / 0.066 mm away#10.1027 in / 2.609 mm away
Letter QLetter gauge0.3320 in8.433 mm
8.4 mm0.0013 in / 0.033 mm away21/64 in0.0039 in / 0.098 mm away#10.1040 in / 2.642 mm away
8.5 mmMetric lookup0.3346 in8.500 mm
Letter Q0.0026 in / 0.067 mm away21/64 in0.0065 in / 0.166 mm away#10.1066 in / 2.709 mm away
8.6 mmMetric lookup0.3386 in8.600 mm
Letter R0.0004 in / 0.011 mm away11/32 in0.0052 in / 0.131 mm away#10.1106 in / 2.809 mm away
Letter RLetter gauge0.3390 in8.611 mm
8.6 mm0.0004 in / 0.011 mm away11/32 in0.0047 in / 0.121 mm away#10.1110 in / 2.819 mm away
8.7 mmMetric lookup0.3425 in8.700 mm
11/32 in0.0012 in / 0.031 mm awayLetter R0.0035 in / 0.089 mm away#10.1145 in / 2.909 mm away
11/32 inFractional inch0.3438 in8.731 mm
8.7 mm0.0012 in / 0.031 mm awayLetter S0.0042 in / 0.108 mm away#10.1157 in / 2.940 mm away
8.8 mmMetric lookup0.3465 in8.800 mm
Letter S0.0015 in / 0.039 mm away11/32 in0.0027 in / 0.069 mm away#10.1185 in / 3.009 mm away
Letter SLetter gauge0.3480 in8.839 mm
8.8 mm0.0015 in / 0.039 mm away11/32 in0.0042 in / 0.108 mm away#10.1200 in / 3.048 mm away
8.9 mmMetric lookup0.3504 in8.900 mm
Letter S0.0024 in / 0.061 mm away11/32 in0.0066 in / 0.169 mm away#10.1224 in / 3.109 mm away
9.0 mmMetric lookup0.3543 in9.000 mm
Letter T0.0037 in / 0.093 mm away23/64 in0.0050 in / 0.128 mm away#10.1263 in / 3.209 mm away
Letter TLetter gauge0.3580 in9.093 mm
9.1 mm0.0003 in / 0.007 mm away23/64 in0.0014 in / 0.035 mm away#10.1300 in / 3.302 mm away
9.1 mmMetric lookup0.3583 in9.100 mm
Letter T0.0003 in / 0.007 mm away23/64 in0.0011 in / 0.028 mm away#10.1303 in / 3.309 mm away
23/64 inFractional inch0.3594 in9.128 mm
9.1 mm0.0011 in / 0.028 mm awayLetter T0.0014 in / 0.035 mm away#10.1314 in / 3.337 mm away
9.2 mmMetric lookup0.3622 in9.200 mm
23/64 in0.0028 in / 0.072 mm awayLetter T0.0042 in / 0.107 mm away#10.1342 in / 3.409 mm away
9.3 mmMetric lookup0.3661 in9.300 mm
Letter U0.0019 in / 0.047 mm away23/64 in0.0068 in / 0.172 mm away#10.1381 in / 3.509 mm away
Letter ULetter gauge0.3680 in9.347 mm
9.3 mm0.0019 in / 0.047 mm away3/8 in0.0070 in / 0.178 mm away#10.1400 in / 3.556 mm away
9.4 mmMetric lookup0.3701 in9.400 mm
Letter U0.0021 in / 0.053 mm away3/8 in0.0049 in / 0.125 mm away#10.1421 in / 3.609 mm away
9.5 mmMetric lookup0.3740 in9.500 mm
3/8 in0.0010 in / 0.025 mm awayLetter V0.0030 in / 0.076 mm away#10.1460 in / 3.709 mm away
3/8 inFractional inch0.3750 in9.525 mm
9.5 mm0.0010 in / 0.025 mm awayLetter V0.0020 in / 0.051 mm away#10.1470 in / 3.734 mm away
Letter VLetter gauge0.3770 in9.576 mm
9.6 mm0.0010 in / 0.024 mm away3/8 in0.0020 in / 0.051 mm away#10.1490 in / 3.785 mm away
9.6 mmMetric lookup0.3780 in9.600 mm
Letter V0.0010 in / 0.024 mm away3/8 in0.0030 in / 0.075 mm away#10.1500 in / 3.809 mm away
9.7 mmMetric lookup0.3819 in9.700 mm
Letter W0.0041 in / 0.104 mm away3/8 in0.0069 in / 0.175 mm away#10.1539 in / 3.909 mm away
9.8 mmMetric lookup0.3858 in9.800 mm
Letter W0.0002 in / 0.004 mm away25/64 in0.0048 in / 0.122 mm away#10.1578 in / 4.009 mm away
Letter WLetter gauge0.3860 in9.804 mm
9.8 mm0.0002 in / 0.004 mm away25/64 in0.0046 in / 0.117 mm away#10.1580 in / 4.013 mm away
9.9 mmMetric lookup0.3898 in9.900 mm
25/64 in0.0009 in / 0.022 mm awayLetter W0.0038 in / 0.096 mm away#10.1618 in / 4.109 mm away
25/64 inFractional inch0.3906 in9.922 mm
9.9 mm0.0009 in / 0.022 mm awayLetter W0.0046 in / 0.117 mm away#10.1626 in / 4.131 mm away
10.0 mmMetric lookup0.3937 in10.000 mm
25/64 in0.0031 in / 0.078 mm awayLetter X0.0033 in / 0.084 mm away#10.1657 in / 4.209 mm away
Letter XLetter gauge0.3970 in10.084 mm
10.1 mm0.0006 in / 0.016 mm away25/64 in0.0064 in / 0.162 mm away#10.1690 in / 4.293 mm away
10.1 mmMetric lookup0.3976 in10.100 mm
Letter X0.0006 in / 0.016 mm away25/64 in0.0070 in / 0.178 mm away#10.1696 in / 4.309 mm away
10.2 mmMetric lookup0.4016 in10.200 mm
Letter Y0.0024 in / 0.062 mm away13/32 in0.0047 in / 0.119 mm away#10.1736 in / 4.409 mm away
Letter YLetter gauge0.4040 in10.262 mm
10.3 mm0.0015 in / 0.038 mm away13/32 in0.0022 in / 0.057 mm away#10.1760 in / 4.470 mm away
10.3 mmMetric lookup0.4055 in10.300 mm
13/32 in0.0007 in / 0.019 mm awayLetter Y0.0015 in / 0.038 mm away#10.1775 in / 4.509 mm away
13/32 inFractional inch0.4063 in10.319 mm
10.3 mm0.0007 in / 0.019 mm awayLetter Y0.0022 in / 0.057 mm away#10.1782 in / 4.528 mm away
10.4 mmMetric lookup0.4094 in10.400 mm
13/32 in0.0032 in / 0.081 mm awayLetter Z0.0036 in / 0.090 mm away#10.1814 in / 4.609 mm away
Letter ZLetter gauge0.4130 in10.490 mm
10.5 mm0.0004 in / 0.010 mm away13/32 in0.0067 in / 0.171 mm away#10.1850 in / 4.699 mm away
10.5 mmMetric lookup0.4134 in10.500 mm
Letter Z0.0004 in / 0.010 mm away13/32 in0.0071 in / 0.181 mm away#10.1854 in / 4.709 mm away
10.6 mmMetric lookup0.4173 in10.600 mm
Letter Z0.0043 in / 0.110 mm away27/64 in0.0046 in / 0.116 mm away#10.1893 in / 4.809 mm away
10.7 mmMetric lookup0.4213 in10.700 mm
27/64 in0.0006 in / 0.016 mm awayLetter Z0.0083 in / 0.210 mm away#10.1933 in / 4.909 mm away
27/64 inFractional inch0.4219 in10.716 mm
10.7 mm0.0006 in / 0.016 mm awayLetter Z0.0089 in / 0.225 mm away#10.1939 in / 4.924 mm away
10.8 mmMetric lookup0.4252 in10.800 mm
27/64 in0.0033 in / 0.084 mm awayLetter Z0.0122 in / 0.310 mm away#10.1972 in / 5.009 mm away
10.9 mmMetric lookup0.4291 in10.900 mm
27/64 in0.0073 in / 0.184 mm awayLetter Z0.0161 in / 0.410 mm away#10.2011 in / 5.109 mm away
11.0 mmMetric lookup0.4331 in11.000 mm
7/16 in0.0044 in / 0.112 mm awayLetter Z0.0201 in / 0.510 mm away#10.2051 in / 5.209 mm away
11.1 mmMetric lookup0.4370 in11.100 mm
7/16 in0.0005 in / 0.012 mm awayLetter Z0.0240 in / 0.610 mm away#10.2090 in / 5.309 mm away
7/16 inFractional inch0.4375 in11.112 mm
11.1 mm0.0005 in / 0.012 mm awayLetter Z0.0245 in / 0.622 mm away#10.2095 in / 5.321 mm away
11.2 mmMetric lookup0.4409 in11.200 mm
7/16 in0.0034 in / 0.087 mm awayLetter Z0.0279 in / 0.710 mm away#10.2129 in / 5.409 mm away
11.3 mmMetric lookup0.4449 in11.300 mm
7/16 in0.0074 in / 0.188 mm awayLetter Z0.0319 in / 0.810 mm away#10.2169 in / 5.509 mm away
11.4 mmMetric lookup0.4488 in11.400 mm
29/64 in0.0043 in / 0.109 mm awayLetter Z0.0358 in / 0.910 mm away#10.2208 in / 5.609 mm away
11.5 mmMetric lookup0.4528 in11.500 mm
29/64 in0.0004 in / 0.009 mm awayLetter Z0.0398 in / 1.010 mm away#10.2248 in / 5.709 mm away
29/64 inFractional inch0.4531 in11.509 mm
11.5 mm0.0004 in / 0.009 mm awayLetter Z0.0401 in / 1.019 mm away#10.2251 in / 5.718 mm away
11.6 mmMetric lookup0.4567 in11.600 mm
29/64 in0.0036 in / 0.091 mm awayLetter Z0.0437 in / 1.110 mm away#10.2287 in / 5.809 mm away
11.7 mmMetric lookup0.4606 in11.700 mm
29/64 in0.0075 in / 0.191 mm awayLetter Z0.0476 in / 1.210 mm away#10.2326 in / 5.909 mm away
11.8 mmMetric lookup0.4646 in11.800 mm
15/32 in0.0042 in / 0.106 mm awayLetter Z0.0516 in / 1.310 mm away#10.2366 in / 6.009 mm away
11.9 mmMetric lookup0.4685 in11.900 mm
15/32 in0.0002 in / 0.006 mm awayLetter Z0.0555 in / 1.410 mm away#10.2405 in / 6.109 mm away
15/32 inFractional inch0.4688 in11.906 mm
11.9 mm0.0002 in / 0.006 mm awayLetter Z0.0558 in / 1.416 mm away#10.2407 in / 6.115 mm away
12.0 mmMetric lookup0.4724 in12.000 mm
15/32 in0.0037 in / 0.094 mm awayLetter Z0.0594 in / 1.510 mm away#10.2444 in / 6.209 mm away
12.1 mmMetric lookup0.4764 in12.100 mm
15/32 in0.0076 in / 0.194 mm awayLetter Z0.0634 in / 1.610 mm away#10.2484 in / 6.309 mm away
12.2 mmMetric lookup0.4803 in12.200 mm
31/64 in0.0041 in / 0.103 mm awayLetter Z0.0673 in / 1.710 mm away#10.2523 in / 6.409 mm away
12.3 mmMetric lookup0.4843 in12.300 mm
31/64 in0.0001 in / 0.003 mm awayLetter Z0.0713 in / 1.810 mm away#10.2563 in / 6.509 mm away
31/64 inFractional inch0.4844 in12.303 mm
12.3 mm0.0001 in / 0.003 mm awayLetter Z0.0714 in / 1.813 mm away#10.2564 in / 6.512 mm away
12.4 mmMetric lookup0.4882 in12.400 mm
31/64 in0.0038 in / 0.097 mm awayLetter Z0.0752 in / 1.910 mm away#10.2602 in / 6.609 mm away
12.5 mmMetric lookup0.4921 in12.500 mm
31/64 in0.0078 in / 0.197 mm awayLetter Z0.0791 in / 2.010 mm away#10.2641 in / 6.709 mm away
12.6 mmMetric lookup0.4961 in12.600 mm
1/2 in0.0039 in / 0.100 mm awayLetter Z0.0831 in / 2.110 mm away#10.2681 in / 6.809 mm away
1/2 inFractional inch0.5000 in12.700 mm
12.7 mmsame nominal diameterLetter Z0.0870 in / 2.210 mm away#10.2720 in / 6.909 mm away
12.7 mmMetric lookup0.5000 in12.700 mm
1/2 insame nominal diameterLetter Z0.0870 in / 2.210 mm away#10.2720 in / 6.909 mm away
12.8 mmMetric lookup0.5039 in12.800 mm
1/2 in0.0039 in / 0.100 mm awayLetter Z0.0909 in / 2.310 mm away#10.2759 in / 7.009 mm away
12.9 mmMetric lookup0.5079 in12.900 mm
1/2 in0.0079 in / 0.200 mm awayLetter Z0.0949 in / 2.410 mm away#10.2799 in / 7.109 mm away
13.0 mmMetric lookup0.5118 in13.000 mm
1/2 in0.0118 in / 0.300 mm awayLetter Z0.0988 in / 2.510 mm away#10.2838 in / 7.209 mm away

Metric rows are conversion lookup points, not a claim that every 0.1 mm size is stocked by every manufacturer. “Closest” means only the smallest nominal diameter difference; it does not establish fit, tool tolerance, or safe interchangeability.

Mechanical micrometer checking the smooth shank of a twist drill beside pin gauges and a brass pen tube
Original Turner's Atlas photo illustration. A shank reading represents cutting diameter only on a full-diameter straight-shank drill.
04 / Verify the hardware

Measure the right feature with the right tool.

  1. Read the current kit instruction.

    A Gatsby kit, for example, explicitly calls for 27/64 inch.5 Record separate cap and body sizes before choosing a bit.

  2. Identify the drill construction.

    Do not assume the shank equals the cutting diameter. PSI sells a 27/64-inch pen drill with a 3/8-inch reduced shank.7

  3. Screen the actual tool.

    Use a micrometer on a suitable full-diameter smooth section, or a drill gauge that contacts the drill body. Look for runout, wear, unequal lips, or an unknown regrind.

  4. Test the process in matching scrap.

    Use the same species or casting, workholding, speed, feed, and pecking method. Keep a drill-press vise flat and perpendicular; support the exit when appropriate.8

  5. Gauge the finished bore.

    Use suitable pin gauges when precision matters, or test the actual tube in scrap. Small-hole readings from ordinary caliper inside jaws are only approximate.

  6. Record a successful pairing.

    Keep the exact drill, kit family, blank material, measured bore, adhesive, and result together. That shop record is more useful than a generic “close enough” conversion.

05 / Understand tolerance

The size mark is not a tolerance specification.

A manufacturer may publish a class such as h8 for a particular drill family, as Guhring does for one HSS jobber series.4 That does not make h8 universal, and tool tolerance still does not predict the complete bore.

Tool

Manufacturing and wear

Diameter tolerance, lip symmetry, margin wear, sharpening, coating, and reduced-shank construction belong to the physical drill—not to “27/64” as a bare label.

Machine

Runout and alignment

Chuck error, a bent shank, tailstock offset, fixture alignment, and long-bit flex can make the cut differ from the drill's measured diameter.

Material

Wood and resin response

Fiber spring-back, grain direction, heat, chip packing, resin softness, and exit breakout can change the bore along its length.

Fit

Tube and adhesive

Tube outside diameter, ovality, surface preparation, and adhesive film all matter. There is no universal clearance that suits every kit and glue.

Illustrative measured bore0.2850 in
−
Illustrative tube OD0.2810 in
=
Total diametral clearance0.0040 in
÷ 2
Radial clearance per side0.0020 in

The numbers above demonstrate the equation only; they are not a recommended fit for a particular kit or adhesive.

06 / Diameter is not geometry

The same marked size can cut differently.

Once the diameter is correct, choose a point, flute, length, and shank that match the blank and setup.

General purpose

Twist / jobber

Broad availability and predictable indexing. Deep bores still need chip clearing and adequate flute length.

Open guide →Wood entry

Brad point

A locating center brad and rim spurs can start cleanly in wood; flute capacity may be the limit in a long bore.

Open field guide →Deep bore

Parabolic / pen-maker

More open flutes improve chip travel, but they do not correct size, runout, or alignment errors.

Open field guide →
Heat-sensitive blanks

Acrylic-point grind

A material-specific point may reduce grabbing or chipping. Follow the blank and drill maker's guidance.

Chuck compatibility

Reduced shank

The cutting body is larger than the shank. Measure or gauge the body; the chucking diameter is not the bore callout.

Length class

Jobber, aircraft, or extra long

Longer reach can increase flex. Confirm flute reach and safe shank grip rather than buying length by name alone.

Do not substitute when

Stop treating “nearby” as “equivalent” if…

  • The current instruction names one exact metric, fractional, number, or letter size.
  • Cap and body use different tubes or different drills.
  • The alternate is only the closest chart value and is not manufacturer-approved.
  • The bit is reduced-shank, reground, worn, bent, or of unknown tolerance.
  • A scrap bore produces force-fit, excessive rattle, heat damage, or glue starvation.
  • The conversion has been rounded before comparing the nominal diameters.
Source bench / reviewed August 2026

References and further reading

Conversion standards establish nominal relationships. Drill and kit manufacturers establish their own products, tolerances, and required bores. Check the current instruction sheet before drilling.

01NISTHandbook 44, Appendix B: units and systems of measurement

The U.S. national measurement reference stating that one international inch equals 25.4 millimetres exactly.

Open source ↗02L. S. StarrettPrecision Tools Catalog 33: conversion cards and charts

Manufacturer reference materials for fractional, decimal, metric, number, and letter drill-size comparison.

Open source ↗03Norseman Drill & ToolHSS Jobber Length Drill Bits

Manufacturer overview identifying the #1–#80, A–Z, metric, and fractional sizing systems used for jobber drills.

Open source ↗04GuhringSeries 207 HSS jobber drill

A manufacturer example that publishes an h8 tolerance class—evidence that tolerance belongs to the tool specification, not the size label alone.

Open source ↗05PSI WoodworkingGatsby Pen Kit instructions

A kit-specific instruction requiring a 27/64-inch bore and matching the drill to the supplied tube and bushings.

Open source ↗06PSI WoodworkingStar Spangled Pen Inlay Kit compatibility chart

One official chart using 7 mm, 8 mm, 3/8 inch, 10 mm, 27/64 inch, 10.5 mm, and .492 inch tube families side by side.

Open source ↗07Penn State Industries27/64-inch HSS Drill Bit

A pen drill whose 27/64-inch cutting diameter uses a smaller 3/8-inch shank—an important warning about where to measure.

Open source ↗08PSI WoodworkingSelf-Centering Drilling Center Vise instructions

Official workholding guidance for keeping the blank perpendicular and supporting the exit with scrap.

Open source ↗