British Standard Fine Thread | BSF Thread Chart

British Standard Fine Thread | BSF Thread Chart

  British Standard Fine Thread | BSF Thread

British Standard Fine (BSF) is a screw thread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread. It was used for steel bolts and nuts on much British machinery, including cars, prior to adoption of Unified, and later Metric, standards. For highly stressed conditions, especially in motorcycles, a finer thread, British Standard Cycle (BSC), was used as well.

BSF was developed by R. E. B. Crompton, and his assistant George Field. BSF threads use the 55 degree Whitworth thread form. It was introduced by the British Engineering Standards Association in 1908.

The table shows suitable tapping drill sizes.

  Thread Count (TPI)

TPI stands for Threads Per Inch, Means the total number of threads per inch measured along the length of a fastener. TPI is used only with American fasteners. Metric Fasteners use a thread Pitch. In general, smaller fasteners have finer threads, so the thread count is higher.

  Thread Pitch

Metric fasteners are specified with a thread pitch instead of a thread count. The thread pitch is the distance between threads expressed in millimeters. In general, smaller fasteners have finer thread so they have lower thread pitch.

  BSF Thread Charts

BSF Thread Chart

  British Standard Fine Thread Charts | BSF Thread Charts

Nominal Inch TPI Pitch Thread Depth Major Diameter Effective Diameter Minor Diameter Tap Drill Size (mm)
3/16 32 0.03125 0.02 0.1875 0.1675 0.1475 4.00 mm
7/32 28 0.03571 0.0229 0.2188 0.1959 0.173 4.60 mm
1/4 26 0.03846 0.0246 0.25 0.2254 0.2008 5.30 mm
9/32 26 0.03846 0.0246 0.2812 0.2566 0.232 6.10 mm
5/16 22 0.04545 0.0291 0.3125 0.2834 0.2543 6.80 mm
3/8 20 0.05 0.032 0.375 0.343 0.311 8.30 mm
7/16 18 0.05556 0.0356 0.4375 0.4019 0.3363 9.70 mm
1/2 16 0.0625 0.04 0.5 0.46 0.42 11.10 mm
9/16 16 0.0625 0.04 0.5625 0.5225 0.4825 12.70 mm
5/8 14 0.07143 0.0457 0.625 0.5793 0.5336 14.00 mm
11/1614 0.07143 0.0457 0.6875 0.6418 0.5961 15.50 mm
3/4 12 0.08333 0.0534 0.75 0.6966 0.6432 16.75 mm
7/8 11 0.09091 0.0582 0.875 0.8168 0.7586 19.75 mm
1 10 0.1 0.064 1 0.936 0.872 22.75 mm
1 1/8 9 0.11111 0.0711 1.125 1.0539 0.9828 25.50 mm
1 1/4 9 0.11111 0.0711 1.25 1.1789 1.1078 28.50 mm
1 3/8 8 0.125 0.08 1.375 1.295 1.215 31.50 mm
1 1/2 8 0.125 0.08 1.5 1.42 1.34 34.50 mm

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