British Threads - British Standard Cycle
BSC (British Standard Cycle) Thread Data
This fine thread profile was formulated for, and is well suited to cycle and motorcycle applications. Its fine pitch, allows high torque settings, and resists the tendancy to loosen under vibration, the larger core diameter also gives greater shear strength. Most people think that all cycle threads are 26 tpi pitch. Whilst this is true of all the most popular sizes from 1/4" to 3/4" diameter, other pitches were also used as shown in the tables seen in the CEI section
We have numerous taps and dies in BSC with 20 tpi threads.
Angle of thread = 60°
| Diameter (Inches) | Threads per inch | Pitch (Inch) | Core Diameter (Inch) | Tapping Drill Size |
|---|---|---|---|---|
| 0.125 (1/8th) inch | 40 Tpi | 0.025 | 0.0984 ins | Number Drill 39 0.1004 inch 2.5mm |
| 0.1563 5/32 inch | 32 Tpi | 0.0312 | 0.1231 ins | Number Drill 30 0.126 inch 3.25mm |
| 0.1875 (3/16) inch | 32 Tpi | 0.0312 | 0.1542 ins | Number Drill 23 0.1562 inch 3.97mm |
| 0.250 (1/4) inch | 26 Tpi | 0.0385 | 0.2091 ins | Number Drill 3 0.2188 inch 5.56mm |
| 0.281 (9/32) inch | 26 Tpi | 0.0385 | 0.2403 ins | Letter Drill D 0.2441 inch 6.2 mm |
| 0.3125 (5/16) inch | 26 Tpi | 0.0385 | 0.2715 ins | Letter Drill J 0.2756 inch 7 mm |
| 0.375 (3/8) inch | 26 Tpi | 0.0385 | 0.334 ins | Letter Drill R 0.3368 inch 8.65 mm |
| 0.4375 (7/16) inch | 26 Tpi | 0.0385 | 0.3965 ins | Letter Drill X 0.3976 inch 10.1 mm |
| 0.5 (1/2) inch | 26 Tpi | 0.0385 | 0.4590 ins | 0.4606 inch 11.7 mm |
| 0.5625 (9/16) inch | 26 Tpi | 0.0385 | 0.5215 ins | 0.5156 (33/64) inch 13.1 mm |
| 0.625 (5/8) inch | 26 Tpi | 0.0385 | 0.5840 ins | 0.5906 inch 15 mm |
| 0.6875 (11/16) inch | 26 Tpi | 0.0385 | 0.6465 ins | 0.6496 inch 16.5 mm |
| 1 inch | 26 Tpi | 0.0385 | 0.959 ins | 0.9688 (31/32) inch 24.61.1 mm |