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Screw Thread Tapping Drill Size Chart for Mechanical Engineers

Ever struggled to find the right drill size for tapping screw threads? This guide demystifies the process with a comprehensive chart, detailing metric, UNC, and fine thread sizes. Whether you’re working on a precise engineering project or everyday mechanical tasks, this article will equip you with the exact measurements you need. Dive in to ensure your tapping jobs are accurate and efficient!

Screw Thread Tapping Drill Size Chart for Mechanical Engineers

Table Of Contents

Screw Thread Tapping Drill Size Chart for Mechanical Engineers

1. Metric Coarse Thread

GradeNominal diameter2nd class tap drill size
MaxMin
M1.0×0.250.75 0.785 0.729 
M1.1×0.250.85 0.885 0.829 
M1.2×0.250.95 0.985 0.985 
M1.4×0.31.10 1.142 1.075 
M1.6×0.351.25 1.321 1.221 
M1.7×0.351.35 1.421 1.321 
M1.8×0.351.45 1.521 1.421 
M2.0×0.41.60 1.679 1.567 
M2.2×0.451.75 1.838 1.713 
M2.3×0.41.90 1.979 1.867 
M2.5×0.452.10 2.138 2.013 
M2.6×0.452.20 2.238 2.113 
M3.0×0.52.50 2.599 2.459 
M3.0×0.62.40 2.440 2.280 
M3.5×0.62.90 3.010 2.850 
M4.0×0.73.30 3.422 3.242 
M4.0×0.753.25 3.326 3.106 
M4.5×0.753.80 3.878 3.688 
M5.0×0.84.20 4.334 4.134 
M5.0×0.94.10 4.170 3.930 
M6.0×1.05.00 5.153 4.917 
M7.0×1.06.00 6.153 5.917 
M8.0×1.256.80 6.912 6.647 
M9.0×1.257.80 7.912 7.647 
M10×1.58.50 8.676 8.376 
M11×1.59.50 9.676 9.376 
M12×1.7510.30 10.441 10.106 
M14×2.012.00 12.210 11.835 
M16×2.014.00 14.210 13.835 
M18×2.515.50 15.744 15.294 
M20×2.517.50 17.744 17.294 
M22×2.519.50 19.744 19.294 
M24×3.021.00 21.252 20.752 
M27×3.024.00 24.252 23.752 
M30×3.526.50 26.771 26.211 

2. UNC (Unified Coarse) Thread

Grade（UNC）Nominal diameter2nd class tap drill size
MaxMin
NO.1-64(1.854)1.55 1.5821.425
NO.2-56(2.184)1.80 1.8711.695
NO.3-48(2.515)2.10 2.1461.941
NO.4-40(2.845)2.30 2.3852.157
NO.5-40(3.175)2.60 2.6972.487
NO.6-32(3.505)2.80 2.8952.642
NO8-32(4.166)3.40 3.533.302
NO.10-24(4.826)3.90 3.9623.683
NO.12-24(5.486)4.50 4.5974.344
1/4-205.10 5.2574.979
5/16-186.60 6.7316.401
3/8-168.00 8.1537.798
7/16-149.40 9.559.144
1/2-1310.80 11.02310.592
9/16-1212.20 12.44611.989
5/8-1113.60 12.86813.386
3/4-1016.50 18.840 16.307
7/8-919.50 19.761 19.177
122.20 22.606 21.971
1-1/8-725.00 25.349 24.638
1-1/4-728.20 28.524 27.813
1-3/8-630.80 31.115 30.353
1-1/2-634.00 34.290 33.528
1-3/4-539.50 39.827 38.964
2-4-1/245.20 45.593 44.679

3. Metric Fine Thread

GradeNominal diameter2nd class tap drill size
MaxMin
M1.0×0.20.80 0.8210.783
M1.1×0.20.90 0.9210.883
M1.2×0.21.00 1.0210.983
M1.4×0.21.20 1.2211.183
M1.6×0.21.40 1.4211.383
M1.7×0.21.45 1.500 1.460 
M1.8×0.21.60 1.621 1.583 
M2.0×0.251.75 1.785 1.729 
M2.2×0.251.95 1.985 1.929 
M2.3×0.252.05 2.061 2.001 
M2.5×0.352.20 2.221 2.121 
M2.6×0.352.20 2.246 2.186 
M3.0×0.352.70 2.721 2.621 
M3.5×0.353.20 3.221 3.121 
M4.0×0.53.50 3.599 3.459 
M4.5×0.54.00 4.099 3.959 
M5.0×0.54.50 4.599 4.459 
M5.5×0.55.00 5.099 4.959 
M6.0×0.755.30 5.378 5.188 
M6.0×0.55.50 5.550 5.400 
M7.0×0.756.30 6.378 6.188 
M7.0×0.56.50 6.550 6.400 
M8.0×1.07.00 7.153 6.917
M8.0×0.757.30 7.378 7.188
M8.0×0.57.50 7.520 7.400 
M9.0×1.08.00 8.153 7.917 
M9.0×0.758.30 8.378 8.188 
M10×1.258.80 8.912 8.647 
M10×1.09.00 9.153 8.917 
M10×0.759.30 9.378 9.188 
M10×0.59.50 9.520 9.400 
M11×1.010.00 10.153 9.917 
M11×0.7510.30 10.378 10.188 
M12×1.510.50 10.676 10.376 
M12×1.2510.80 10.912 10.647 
M12×1.011.00 11.153 10.917 
M12×0.511.50 11.520 11.400 
M14×1.512.50 12.676 12.376 
M14×1.013.00 13.153 12.917 
M15×1.513.50 13.676 13.376 
M15×1.014.00 14.153 13.917 
M16×1.514.50 14.676 14.376 
M16×1.015.00 15.153 14.917 
M17×1.515.50 15.676 15.376 
M17×1.016.00 16.153 15.917 
M18×2.016.00 16.210 15.835 
M18×1.516.50 16.676 16.376 
M18×1.017.00 17.153 16.917 
M20×2.018.00 18.210 17.835 
M20×1.518.50 18.676 18.376 
M20×1.019.00 19.153 18.917 
M22×2.020.00 20.210 19.835 
M22×1.520.50 20.676 20.376 
M22×1.021.00 21.153 20.917 
M24×2.022.00 22.210 21.835 
M24×1.522.50 22.676 22.376 
M24×1.023.00 23.153 22.917 
M25×2.023.00 23.210 22.835 
M25×1.523.50 23.676 23.376 
M25×1.024.00 24.153 23.917 
M26×1.524.50 24.676 24.376 
M27×2.025.00 25.210 24.835 
M27×1.525.50 25.676 25.376 
M27×1.026.00 26.153 25.917 
M28×2.026.00 26.210 25.835 
M28×1.526.50 26.676 26.376 
M28×1.027.00 27.15326.917
M30×3.027.00 27.25226.752
M30×2.028.00 28.210 27.835
M30×1.528.50 28.676 28.376
M30×1.029.00 29.153 28.917
M32×2.030.00 30.210 29.835
M32×1.530.50 30.676 30.376
M33×3.030.00 30.252 29.752
M33×2.031.00 31.210 30.835
M33×1.531.50 31.676 31.376
M35×1.533.50 33.676 33.376
M36×3.033.00 33.252 32.752
M36×2.034.00 34.210 33.835
M36×1.534.50 34.676 34.376

4. Unified Fine Thread

Grade（UNC）Nominal diameter2nd class tap drill size
MaxMin
NO.0-80(1.524)1.25 1.3051.182
NO.1-72(1.854)1.55 1.6121.474
NO.2-64(2.184)1.85 1.9121.756
NO.3-56(2.515)2.10 2.1972.025
NO.4-48(2.845)2.40 2.4582.271
NO.5-44(3.175)2.70 2.740 2.551
NO.6-40(3.505)2.90 3.022 2.820 
NO.8-36(4.166)3.50 3.606 3.404 
NO.10-32(4.826)4.10 4.165 3.963 
NO.12-28(5.846)4.60 4.724 4.496 
1/4-285.50 5.588 5.360 
5/16-246.90 7.035 6.782 
3/8-248.50 8.636 8.382 
7/16-209.90 10.033 9.729 
1/2-2011.50 11.607 11.329 
9/16-1812.90 13.081 12.751 
5/8-1814.50 14.681 14.351 
3/4-1617.50 17.678 17.323 
7/8-1420.50 20.675 20.270 
1-1223.20 23.571 23.114 
1-1/8-1226.50 26.746 26.289 
1-1/4-1229.50 29.921 29.464 
1-3/8-1232.80 33.09632.639
1-1/2-1236.00 36.27135.814

5. Metric thread tap drill diameter

GradeAccuracy level
G4-G6G7-G8G9
M1.0×0.250.860.88－
M1.1×0.250.960.98－
M1.2×0.251.061.08－
M1.4×0.31.241.25－
M1.6×0.351.411.43－
M1.7×0.351.511.53－
M1.8×0.351.611.63－
M2.0×0.41.781.80 －
M2.2×0.451.951.98 －
M2.3×0.42.082.10 －
M2.5×0.452.252.28 －
M2.6×0.452.352.38 －
M3.0×0.52.732.75 －
M3.5×0.63.173.20 －
M4.0×0.73.623.65 3.69
M5.0×0.84.564.60 4.64
M6.0×1.05.455.50 5.55
M7.0×1.06.456.50 6.55
M8.0×1.257.317.38 7.44
M10×1.59.189.25 9.32
M10×1.259.319.38 9.44
M12×1.7511.0411.12 11.21
M12×1.2511.3111.38 11.44

6. Imperial thread tap drill diameter

GradeAccuracy level
G4-G6G7-G8G9
NO.2-56UNC1.94 －－
NO.3-482.23 －－
NO.4-402.50 －－
NO.5-402.83 －－
NO.6-323.07 －－
NO.8-323.73 3.77－
NO.10-244.24 4.3－
NO.12-244.90 4.96－
1/4-20－5.72－
5/16-18－7.24－
3/8-16－8.748.81
7/16-14－10.20 10.30 
1/2-13－11.27 11.82
NO.2-64UNF1.97 －－
NO.3-562.27 －－
NO.4-482.56 －－
NO.5-442.86 －－
NO.6-403.16 －－
NO.8-363.78 －－
NO.10-324.39 4.43 －
NO.12-284.99 5.04 －
1/4-285.85 5.90 －
5/16-247.36 7.41 －
3/8-24－9.00 －
7/16-20－10.48 10.54
1/2-20－12.07 12.13

7. American standard fine thread and British standard electrical thread

American standard fine thread
Grade(UNEF)Nominal diameter2nd class tap drill size
MaxMin
NO.12-324.70 4.826 4.623 
1/4     -325.60 5.690 5.486 
5/16   -327.10 7.264 7.087 
3/8    -328.70 8.865 8.661 
7/16   -2810.20 10.338 10.135 
1/2     -2811.80 11.938 11.709 
9/16    -2413.20 13.386 13.132 
5/8    -2414.80 14.986 14.732 
3/4    -2017.80 17.958 17.678 
7/8    -2021.00 21.133 20.853 
1      -2024.00 24.308 24.028 
British standard electrical thread
GradeDrilling diameter
2BA4.0-4.2
3BA
4BA3.0-3.2
5BA2.7-2.8
6BA2.4-2.5

8. Pipe thread

English pipe threadEnglish pipe threadAmerican pipe thread
GradeStandard diameterDrilling hole diameterGradeStandard diameterthe minimum inner diameter of the non-threaded portion with the length of the intersecting teeth (minimum)the minimum inner diameter of the non-threaded portion with the standard length (minimum)GradeDrilling hole diameter
MaxMinwhen using a threading toolwhen not using a threading toolNPTNPS
when using a threading toolwhen not using a threading tool
PS 1/16 – 286.50 6.6326.490 PT 1/16 – 286.10 6.20 6.2446.3841/16 – 276.10 6.25 6.35 
PS 1/8 – 288.50 8.6378.495 PT 1/8 – 288.10 8.20 8.2498.3881/8 – 278.33 8.43 8.74 
PS 1/4 – 1911.40 11.54911.341 PT 1/4 – 1910.70 11.00 10.96211.1741/4 – 1810.72 11.13 11.13 
PS 3/8 – 1915.00 15.05414.846 PT 3/8 – 1914.20 14.50 14.44814.6583/8 – 1814.27 14.27 14.68 
PS 1/2 – 1418.50 18.77318.489 PT 1/2 – 1417.60 18.00 17.97918.2631/2 – 1417.48 17.86 18.26 
PS 3/4 -1424.00 24.25923.975 PT 3/4 – 1423.00 23.50 23.37823.6633/4 – 1422.63 23.01 23.42 
PS 1 – 1130.20 30.47130.111 PT 1- 1129.00 29.50 29.45929.8221 – 11-1/228.58 28.98 29.36 
PS 1-1/4 – 1138.80 39.13238.772 PT 1-1/4 – 1137.50 38.00 37.97638.3391-1/4-11-1/237.31 37.69 38.10 
PS 1-1/2 – 1144.80 45.02544.665 PT 1-1/2 – 1143.40 44.00 43.86944.2321-1/2-11-1/243.66 44.04 44.45 
PS 2 – 1156.50 56.83656.476 PT 2 – 1154.90 55.50 55.41255.8442 – 11 – 1/255.58 55.96 56.36 

9. Thread and needle for sewing machine.

Imperial threadMetric threadThread for needle car
Grade (UNEF)Drill diameterGradeRolling diameterGradeRolling diameter
Hard materialSoft material
W 1/8 – 402.65 2.60 M3×0.52.63-2.60SM1/8-402.735-2.688
W 5/32 – 323.25 3.20 M3.0×0.62.56-2.53SM1/8-442.769-2.722
W 3/16  – 243.75 3.70 M3.5×0.63.06-3.03SM9/64-403.128-3.083
W 1/4 – 205.10 5.00 M4.0×0.73.49-3.45SM11/64-403.855-3.805
W 5/16 – 186.60 6.50 M4.0×0.753.45-3.41SM3/16-324.205-4.155
W 3/8 – 168.00 7.90 M4.5×0.753.96-3.92SM3/16-284.143-4.093
W 7/16 – 149.40 9.30 M5.0×0.84.43-4.38SM7/32-325.003-4.955
W 1/2 – 1210.70 10.50 M5.0×0.94.36-4.31SM15/64-285.325-5.570
W 9/16 – 1212.30 12.00 M6.0×1.05.30-5.25SM1/4-405.890-5.735
W 5/8 – 1113.70 13.50 M7.0×1.06.30-6.25SM1/4-285.721-5.366
W 3/4 – 1016.70 16.50 M8.0×1.07.28-7.23SM9/32-286.508-6.648
W 7/8 – 919.50 19.30 M8.0×1.257.12-7.07SM11/32-288.092-8.432
W1 – 822.40 22.00 SM3/8-288.880-8.015
W 1-1/8 – 725.00 24.80 SM7/16-2810.466-10.401
W 1 – 1/4 – 728.30 28.00 SM7/16-1610.037-9.967
SM1/2-2011.819-11.749
SM9/26-2013.400-13.425

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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