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British Standard Cycle Thread

British Standard Cycle is a British Imperial screw thread standard

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British Standard Cycle is a British Imperial screw thread standard made for bicycle and motorcycle applications.

Outside Diameter
1/4 26 0.0385 0.250 0.209
5/16 26 0.0385 0.3125 0.272
3/8 26 0.0385 0.3750 0.334
7/16 26 0.0385 0.4375 0.397
1/2 26 0.0385 0.5000 0.459
9/16 26 0.0385 0.5625 0.522
5/8 26 0.0385 0.6250 0.584
11/16 26 0.0385 0.6875 0.647
3/4 26 0.0385 0.7500 0.709
1 26 0.0385 1 0.959
1 3/8 24 0.0417 1.625 1.326
  • TPI = threads per inch
  • the thread angle is 60 degrees

The fine pitch allows high torque settings and is resistant to vibrations.

bicycle bottom bracket

Note that the most commonly used bottom bracket thread today is 1 3/8" x 24 TPI.

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