Thread Size Table

Sometimes I find I myself with a screw-thread I need to match, but a standard (metric) nut or bolt doesn't fit. It's clearly from some antediluvian thread class like BSF or UNC, but it's not always obvious which. My usual default is to drill it out and rethread or heli-coil it with a modern metric thread, but it's not always possible.

This table is intended to be a handy way to measure diameter and pitch and work out which thread you're looking at. It also includes tapping drill sizes (calculated as diameter minus pitch). Where multiple thread types have the same diameter and pitch (e.g. BSW 3/8"-16 and UNC 3/8"-16), you're on your own.

If you'd like a copy of this table as a spreadsheet in ODS, CSV or XLSX format, please get in touch (specifying your preferred format).

  Only show metric threads
  Only show coarse threads
  Only show conduit/pipe threads

Outer Diameter (mm)Pitch (mm)TPI (where relevant)Tap Drill Size (mm)Thread ClassThread Name
0.790.190.6BA16 BA
0.900.210.7BA15 BA BA BA
1.300.281.1BA12 BA
1.500.311.2BA11 BA
1.520.32801.3UNFUNF #0-80
1.700.351.4BA10 BA
1.850.35721.6UNFUNF #1-72
1.850.40641.5UNCUNC #1-64
1.900.391.6BA9 BA FineM2×0.25 (Fine)
2.000.401.6Metric CoarseM2×0.4
2.180.40641.8UNFUNF #2-64
2.180.45561.8UNCUNC #2-56
2.200.431.8BA8 BA
2.500.352.2Metric FineM2.5×0.35 (Fine)
2.500.452.1Metric CoarseM2.5×0.45
2.500.482.1BA7 BA
2.510.45562.1UNFUNF #3-56
2.510.53482.0UNCUNC #3-48
2.800.532.3BA6 BA
2.840.53482.4UNFUNF #4-48
2.840.64402.3UNCUNC #4-40
3.000.352.7Metric FineM3×0.35 (Fine)
3.000.502.5Metric CoarseM3×0.5
3.180.58442.6UNFUNF #5-44
3.180.64402.6BSWBSW 1/8"-40
3.180.64402.6UNCUNC #5-40
3.200.592.7BA5 BA
3.500.353.2Metric FineM3.5×0.35 (Fine)
3.500.602.9Metric CoarseM3.5×0.6
3.510.64402.9UNFUNF #6-40
3.510.79322.8UNCUNC #6-32
3.600.663.0BA4 BA
4.000.503.5Metric FineM4×0.5 (Fine)
4.000.703.3Metric CoarseM4×0.7
4.100.733.4BA3 BA
4.170.71363.5UNFUNF #8-36
4.170.79323.4UNCUNC #8-32
4.700.813.9BA2 BA
4.760.79324.0BSFBSF 3/16"-32
4.761.06243.8BSWBSW 3/16"-24
4.830.79324.1UNFUNF #10-32
4.831.06243.8UNCUNC #10-24
5.000.504.5Metric FineM5×0.5 (Fine)
5.000.804.2Metric CoarseM5×0.8
5.300.904.4BA1 BA
5.490.91284.6UNFUNF #12-28
5.491.06244.5UNCUNC #12-24
5.560.91284.7BSFBSF 7/32"-28
6.000.755.3Metric FineM6×0.75 (Fine) BA CoarseM6×1
6.350.91285.5UNFUNF 1/4"-28
6.350.98265.4BSFBSF 1/4"-26
6.351.27205.1BSWBSW 1/4"-20
6.351.27205.1UNCUNC 1/4"-20
7.140.98266.2BSFBSF 9/32"-26
7.941.06246.9UNFUNF 5/16"-24
7.941.15226.8BSFBSF 5/16"-22
7.941.41186.6BSWBSW 5/16"-18
7.941.41186.6UNCUNC 5/16"-18
8.000.757.3Metric Extra FineM8×0.75 (Extra Fine) FineM8×1 (Fine) CoarseM8×1.25
9.531.06248.5UNFUNF 3/8"-24
9.531.27208.3BSFBSF 3/8"-20
9.531.59168.0BSWBSW 3/8"-16
9.531.59168.0UNCUNC 3/8"-16
9.730.91288.6BSPBSP 1/8"-28 Extra FineM10×1 (Extra Fine) FineM10×1.25 (Fine)
10.001.508.5Metric CoarseM10×1.5
10.290.94278.6NPTNPT 1/8"-27
11.111.27209.9UNFUNF 7/16"-20
11.111.41189.8BSFBSF 7/16"-18
11.111.81149.3BSWBSW 7/16"-14
11.111.81149.3UNCUNC 7/16"-14
12.001.5010.5Metric FineM12×1.5 (Fine)
12.001.7510.3Metric CoarseM12×1.75
12.701.272011.5UNFUNF 1/2"-20
12.701.411811.3BSConBSCon 1/2"-18
12.701.591611.2BSFBSF 1/2"-16
12.701.951310.8UNCUNC 1/2"-13
12.702.121210.6BSWBSW 1/2"-12
13.161.341911.5BSPBSP 1/4"-19
13.721.411811.1NPTNPT 1/4"-18
14.001.5012.5Metric FineM14×1.5 (Fine)
14.002.0012.0Metric CoarseM14×2
14.291.411812.9UNFUNF 9/16"-18
14.291.591612.7BSFBSF 9/16"-16
14.292.121212.2BSWBSW 9/16"-12
14.292.121212.2UNCUNC 9/16"-12
15.881.411814.5UNFUNF 5/8"-18
15.881.411814.5BSConBSCon 5/8"-18
15.881.811414.1BSFBSF 5/8"-14
15.882.311113.6BSWBSW 5/8"-11
15.882.311113.6UNCUNC 5/8"-11
16.001.5014.5Metric FineM16×1.5 (Fine)
16.002.0014.0Metric CoarseM16×2
16.661.341915.0BSPBSP 3/8"-19
17.151.411814.7NPTNPT 3/8"-18
17.461.811415.7BSFBSF 11/16"-14
17.462.311115.2BSWBSW 11/16"-11
18.001.5016.5Metric Extra FineM18×1.5 (Extra Fine)
18.002.0016.0Metric FineM18×2 (Fine)
18.002.5015.5Metric CoarseM18×2.5
19.051.591617.5UNFUNF 3/4"-16
19.051.591617.5BSConBSCon 3/4"-16
19.052.121217.0BSFBSF 3/4"-12
19.052.541016.6BSWBSW 3/4"-10
19.052.541016.6UNCUNC 3/4"-10
20.001.5018.5Metric Extra FineM20×1.5 (Extra Fine)
20.002.0018.0Metric FineM20×2 (Fine)
20.002.5017.5Metric CoarseM20×2.5
20.961.811418.7BSPBSP 1/2"-14
21.341.811418.3NPTNPT 1/2"-14
22.001.5020.5Metric Extra FineM22×1.5 (Extra Fine)
22.002.0020.0Metric FineM22×2 (Fine)
22.002.5019.5Metric CoarseM22×2.5
22.231.811420.5UNFUNF 7/8"-14
22.232.311120.0BSFBSF 7/8"-11
22.232.82919.5BSWBSW 7/8"-9
22.232.82919.5UNCUNC 7/8"-9
22.911.811420.7BSPBSP 5/8"-14
24.002.0022.0Metric FineM24×2 (Fine)
24.003.0021.0Metric CoarseM24×3
25.401.591623.9BSConBSCon 1"-16
25.402.121223.3UNFUNF 1"-12
25.402.541022.9BSFBSF 1"-10
25.403.18822.3BSWBSW 1"-8
25.403.18822.3UNCUNC 1"-8
26.441.811424.2BSPBSP 3/4"-14
26.671.811423.4NPTNPT 3/4"-14
27.002.0025.0Metric FineM27×2 (Fine)
27.003.0024.0Metric CoarseM27×3
30.002.0028.0Metric FineM30×2 (Fine)
30.003.5026.5Metric CoarseM30×3.5

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