BSC (British Standard Cycle) Thread Data

Click Here for Thread Profile Drawing

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 ¼¨ to ¾¨ diameter, other pitches were also used as shown in the tables.

Angle of thread = 60o
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

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