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BSF Fine Threads (BS 84)

The BSF is the Fine Thread series of British Standard 84:1956 - Parallel Screw Threads of Whitworth Form. The dimensions given in the tables on the following pages for the major, effective, and minor diameters are, respectively, the maximum limits of these diameters for bolts and the minimum limits for nuts.

3/16" - 1 3/4" 2" - 4 1/4"

Nominal Size BSF Thread Form Type Major Diameter mm d=D Pitch mm p Threads per inch tpi Pitch Diameter mm d2=D2 Minor Diameter Male Thd. d3 Thread Height H1 Tap Drill Diameter mm
3/16" BSF 4.763 0.794 32 4.255 3.747 0.508 4.00
7/32" BSF 5.556 0.907 28 4.975 4.394 0.581 4.60
1/4" BSF 6.350 0.977 26 5.725 5.100 0.625 5.30
9/32" BSF 7.142 0.977 26 6.518 5.893 0.625 6.10
5/16" BSF 7.938 1.156 22 7.199 6.459 0.739 6.80
3/8" BSF 9.525 1.27 20 8.712 7.899 0.813 8.30
7/16" BSF 11.113 1.411 18 10.209 9.304 0.904 9.70
1/2" BSF 12.700 1.588 16 11.684 10.668 1.017 11.10
9/16" BSF 14.288 1.588 16 13.272 12.256 1.017 12.70
5/8" BSF 15.875 1.814 14 14.712 13.549 1.162 14.00
11/16" BSF 17.463 1.814 14 16.300 15.137 1.162 15.50
3/4" BSF 19.050 2.117 12 17.693 16.336 1.355 16.75
13/16" BSF 20.638 2.117 12 19.281 17.924 1.355 18.25
7/8" BSF 22.225 2.309 11 20.747 19.269 1.479 19.75
1" BSF 25.400 2.54 10 23.774 22.148 1.627 22.75
1 1/8" BSF 28.575 2.822 9 26.769 24.963 1.807 26.50
1 1/4" BSF 31.750 2.822 9 29.944 28.138 1.807 28.75
1 3/8" BSF 34.925 3.175 8 32.893 30.861 2.033 31.50
1 1/2" BSF 38.100 3.175 8 36.068 34.036 2.033 34.50
1 5/8" BSF 41.275 3.175 8 39.243 37.211 2.033 38.00
1 3/4" BSF 44.450 3.629 7 42.126 39.802 2.324 40.50
2" BSF 50.800 3.629 7 48.476 46.152 2.324 47.00
2 1/4" BSF 57.150 4.234 6 54.440 51.730 2.711 53.00
2 1/2" BSF 63.500 4.234 6 60.790 58.080 2.711 59.00
2 3/4" BSF 69.850 4.234 6 67.140 64.430 2.711 n/a
3" BSF 76.200 5.08 5 72.946 69.692 3.253 n/a
3 1/4" BSF 82.550 5.08 5 79.296 76.042 3.253 n/a
3 1/2" BSF 88.900 5.645 4 1/2 85.285 81.670 3.614 n/a
3 3/4" BSF 95.250 5.645 4 1/2 91.635 88.020 3.614 n/a
4" BSF 101.600 5.645 4 1/2 97.985 94.370 3.614 n/a
4 1/4" BSF 107.950 6.35 4 103.886 99.822 4.066 n/a
  • BSW & BSF thread notes:
  • C = Core diameter = Major Diameter - 1.280654 x P
  • d = Actual Depth = 0.640327 x P
  • D = Depth of Rounding = 0.073917 x P
  • Effective or Pitch Diameter = Major Diameter - .640327 x P
  • h = Angular Depth = 0.960491 x P
  • h/6 = Shortening = 0.160083 x P
  • P = Pitch = 1/Number of threads per inch (tpi)
  • r = Radius at the Crest & Root = 0.137329 x P