BSF Threads British Standard Fine fastener threads
BSF fasteners
Threaded fasteners, bolts, nuts, screws and fastenings in BSF British Standard Fine (BSF) is a screw thread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread
| BSF..... | Nominal | TPI Threads per inch | PITCH | Major Diameter | Pitch Diameter | Minor Diameter male thread | Thread Height female thread | Tap Drill |
|---|---|---|---|---|---|---|---|---|
| P | d=D | d2=D2 | d3 | H1 | ||||
| 3/16" | 0.188 | 32 | 0.0313 | 0.1875 | 0.1675 | 0.1475 | 0.0200 | 0.1575 |
| 7/32" | 0.219 | 28 | 0.0357 | 0.2187 | 0.1959 | 0.1730 | 0.0229 | 0.1811 |
| 1/4" | 0.250 | 26 | 0.0385 | 0.2500 | 0.2254 | 0.2008 | 0.0246 | 0.2087 |
| 9/32" | 0.281 | 26 | 0.0385 | 0.2812 | 0.2566 | 0.2320 | 0.0246 | 0.2402 |
| 5/16" | 0.313 | 22 | 0.0455 | 0.3125 | 0.2834 | 0.2543 | 0.0291 | 0.2677 |
| 3/8" | 0.375 | 20 | 0.0500 | 0.3750 | 0.3430 | 0.3110 | 0.0320 | 0.3268 |
| 7/16" | 0.438 | 18 | 0.0556 | 0.4375 | 0.4019 | 0.3663 | 0.0356 | 0.3819 |
| 1/2" | 0.500 | 16 | 0.0625 | 0.5000 | 0.4600 | 0.4200 | 0.0400 | 0.4370 |
| 9/16" | 0.563 | 16 | 0.0625 | 0.5625 | 0.5225 | 0.4825 | 0.0400 | 0.5000 |
| 5/8" | 0.625 | 14 | 0.0714 | 0.6250 | 0.5792 | 0.5334 | 0.0457 | 0.5512 |
| 11/16" | 0.688 | 14 | 0.0714 | 0.6875 | 0.6417 | 0.5959 | 0.0457 | 0.6102 |
| 3/4" | 0.750 | 12 | 0.0833 | 0.7500 | 0.6966 | 0.6431 | 0.0533 | 0.6594 |
| 13/16" | 0.813 | 12 | 0.0833 | 0.8125 | 0.7591 | 0.7057 | 0.0533 | 0.7185 |
| 7/8" | 0.875 | 11 | 0.0909 | 0.8750 | 0.8168 | 0.7586 | 0.0582 | 0.7776 |
| 1" | 1.000 | 10 | 0.1000 | 1.0000 | 0.9360 | 0.8720 | 0.0641 | 0.8957 |
| 1 1/8" | 1.125 | 9 | 0.1111 | 1.1250 | 1.0539 | 0.9828 | 0.0711 | 1.0433 |
| 1 1/4" | 1.250 | 9 | 0.1111 | 1.2500 | 1.1789 | 1.1078 | 0.0711 | 1.1319 |
| 1 3/8" | 1.375 | 8 | 0.1250 | 1.3750 | 1.2950 | 1.2150 | 0.0800 | 1.2402 |
| 1 1/2" | 1.500 | 8 | 0.1250 | 1.5000 | 1.4200 | 1.3400 | 0.0800 | 1.3583 |
| 1 5/8" | 1.625 | 8 | 0.1250 | 1.6250 | 1.5450 | 1.4650 | 0.0800 | 1.4961 |
| 1 3/4" | 1.750 | 7 | 0.1429 | 1.7500 | 1.6585 | 1.5670 | 0.0915 | 1.5945 |
| 2" | 2.000 | 7 | 0.1429 | 2.0000 | 1.9085 | 1.8170 | 0.0915 | 1.8504 |
| 2 1/4" | 2.250 | 6 | 0.1667 | 2.2500 | 2.1433 | 2.0366 | 0.1067 | 2.0866 |
| 2 1/2" | 2.500 | 6 | 0.1667 | 2.5000 | 2.3933 | 2.2866 | 0.1067 | 2.3228 |
| 2 3/4" | 2.750 | 6 | 0.1667 | 2.7500 | 2.6433 | 2.5366 | 0.1067 | 2.5463 |
| 3" | 3.000 | 5 | 0.2000 | 3.0000 | 2.8719 | 2.7438 | 0.1281 | 2.7778 |
| 3 1/4" | 3.250 | 5 | 0.2000 | 3.2500 | 3.1219 | 2.9938 | 0.1281 | 3.0093 |
| 3 1/2" | 3.500 | 4 1/2 | 0.2222 | 3.5000 | 3.3577 | 3.2154 | 0.1423 | 3.2407 |
| 3 3/4" | 3.750 | 4 1/2 | 0.2222 | 3.7500 | 3.6077 | 3.4654 | 0.1423 | 3.4722 |
| 4" | 4.000 | 4 1/2 | 0.2222 | 4.0000 | 3.8577 | 3.7154 | 0.1423 | 3.7037 |
| 4 1/4" | 4.250 | 4 | 0.2500 | 4.2500 | 4.0900 | 3.9300 | 0.1601 | 3.9352 |
British Standard Fine thread (BSF) is a fine screw thread form, being a fine-pitch alternative to British Standard Whitworth (BSW) that is a coarse thread. BSF threads appear on steel bolts and nuts on British cars and machinery, before the adoption of Unified American threads on cars, and later Metric threads on the majority of new products.
BSF threads were developed by Rookes Crompton, and his assistant George Field in 1908, BSF threads use the same Whitworth 55 degree thread form with more threads per inch.
