Thread StandardsBritish Standard Fine Thread Series (parallel, cylindrical).
BSW and BSF are the Thread selections for commercial screws and nuts. The Fine Thread, which is widespread in the Britisch
machine tool industry, is superseded by the American UNF Thread.
The thread angle is 55°.
| Nominal Diameter |
Major Diameter Inch |
Major Diameter mm |
Tapping Drill Size mm |
TPI | Pitch mm |
| BSF 3/16" | 0.1875 | 4.763 | 3.950 | 32 | 0.794 |
| BSF 7/32" | 0.2188 | 5.556 | 4.600 | 28 | 0.907 |
| BSF 1/4" | 0.2500 | 6.350 | 5.300 | 26 | 0.977 |
| BSF 9/32" | 0.2812 | 7.144 | 6.100 | 26 | 0.977 |
| BSF 5/16" | 0.3125 | 7.938 | 6.750 | 22 | 1.154 |
| BSF 3/8" | 0.3750 | 9.525 | 8.200 | 20 | 1.270 |
| BSF 7/16" | 0.4375 | 11.113 | 9.580 | 18 | 1.411 |
| BSF 1/2" | 0.5000 | 12.700 | 11.100 | 16 | 1.587 |
| BSF 9/16" | 0.5625 | 14.288 | 12.600 | 16 | 1.587 |
| BSF 5/8" | 0.6250 | 15.875 | 13.900 | 14 | 1.814 |
| BSF 11/16" | 0.6875 | 17.463 | 15.500 | 14 | 1.814 |
| BSF 3/4" | 0.7500 | 19.050 | 16.700 | 12 | 2.117 |
| BSF 7/8" | 0.8750 | 22.225 | 19.600 | 11 | 2.309 |
| BSF 1" | 1.0000 | 25.400 | 22.500 | 10 | 2.540 |
| BSF 1 1/8" | 1.1250 | 28.575 | 25.400 | 9 | 2.822 |
| BSF 1 1/4" | 1.2500 | 31.750 | 28.560 | 9 | 2.822 |
| BSF 1 3/8" | 1.3750 | 34.925 | 31.350 | 8 | 3.175 |
| BSF 1 1/2" | 1.5000 | 38.100 | 34.500 | 8 | 3.175 |
| BSF 1 5/8" | 1.6250 | 41.275 | 37.710 | 8 | 3.175 |
| BSF 1 3/4" | 1.7500 | 44.450 | 40.480 | 7 | 3.628 |
| BSF 2" | 2.0000 | 50.800 | 46.830 | 7 | 3.628 |
| BSF 2 1/4" | 2.2500 | 57.150 | 52.400 | 6 | 4.233 |
| BSF 2 1/2" | 2.5000 | 63.500 | 58.740 | 6 | 4.233 |
| BSF 2 3/4" | 2.7500 | 69.850 | 65.000 | 6 | 4.233 |
| BSF 3" | 3.0000 | 76.200 | 70.500 | 5 | 5.080 |
| BSF 3 1/4" | 3.2500 | 82.550 | 79.370 | 5 | 5.080 |
| BSF 3 1/2" | 3.5000 | 88.900 | 82.550 | 4.5 | 5.644 |
| BSF 3 3/4" | 3.7500 | 95.250 | 88.900 | 4.5 | 5.644 |
| BSF 4" | 4.0000 | 101.600 | 95.250 | 4.5 | 5.644 |
| BSF 4 1/4" | 4.2500 | 107.950 | 101.600 | 4 | 6.350 |
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