British Standard Fine

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.[1] BSF threads use the 55 degree Whitworth thread form. It was introduced by the British Engineering Standards Association in 1908.[2]

The table provides BSF sizes, the threads per inch and spanner jaw sizes. The BSC column indicates where BSF and BSC threads match. The table shows suitable tapping drill sizes. Uncommon sizes are shown in italics.

Table
Diameter Thread
density
(threads
per inch/TPI)		 As BSC? Nut Tap drill
(inches) (mm) (in−1) (mm) Approx.
(inches)
​3⁄16 0.19 4.83 32 Yes 8.59 11⁄32 6pt ​5⁄32 in
​7⁄32 0.22 5.59 28 No ? ? 4.6 mm
​1⁄4 0.25 6.35 26 Yes 11.30 -- 5.3 mm
​5⁄16 0.31 7.87 22 No 13.35 17⁄32 ​17⁄64 in
​3⁄8 0.375 9.53 20 15.24 5⁄8 8.2 mm
​7⁄16 0.44 11.18 18 18.03 11⁄16 9.7 mm
​1⁄2 0.50 12.70 16 20.83 13⁄16 ​7⁄16 in
​9⁄16 0.56 14.22 16 23.37 15⁄16 ​1⁄2 in
​5⁄8 0.63 16.00 14 25.65 1 6pt 14 mm
​11⁄16 0.69 17.53 14 27.94 1 1⁄8 6pt 15.5 mm
​3⁄4 0.75 19.05 12 30.48 1 1⁄4 6pt 16.75 mm
​7⁄8 0.88 22.35 11 33.02 1 5⁄16 ​25⁄32 in
1 1.00 25.40 10 37.59 1 1⁄2 22.75 mm
​1 1⁄8 1.13 28.70 9 42.42 1 11⁄16 26.50 mm
​1 1⁄4 1.25 31.75 9 47.24 1 7⁄8 28.75 mm
​1 1⁄2 1.50 38.10 8 56.39 2 1⁄4 34.50 mm

References
  1. Glanfield, John (2001). The Devil's Chariots. Sutton. p. 87. ISBN 0-7509-4152-9.CS1 maint: ref=harv (link)
  2. Sidders 1969, p.16

Bibliography
  • P.A. Sidders, ed. (1969). Guide to World Screw Threads. New York: Industrial Press. ISBN 0-8311-1092-9.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.