British Standard Cycle (BSC)

screw thread series

Sometimes the symbol “BSCy” is used. This series replaced the Cycle Engineers' Institute (CEI) thread. Though the two series are somewhat different, in the early 21st century the BSC series was still sometimes being called the CEI series. For an even earlier thread, see the bottom of the BSW page.

Symmetrical 60° thread angle, with rounded roots and crests having a radius of 0.166 times the pitch. Actual depth, 0.5327 times the pitch. The smaller sizes are for spokes.

Imperial Wire Gauge	Diameter inches	Threads per inch	Tap Drill Size
17	0.056	62	61
16	0.064	62	56
15	0.072	62	54
14	0.080	62	1/16 inch
13	0.920	56	49
12	0.104	44	47
—	0.125	40	2.5 mm
	0.154	40	30
	0.175	32	27
	0.1875	32	23
	0.250	26	4
	0.266	26	1
	0.281	26	C
	0.3125	26	J
	0.375	26	8.5 mm
	0.5625	20	13 mm
	1.000	26	24.5 mm
	1.290	24	1¼ inch
	1.370	24	1 21/64 inch
	1.4375	24	35.5 mm
	1.500	24	37 mm

British Standard 811-1938. British Standard Cycle (B.S.C.) Threads.

Fasteners with these threads can be obtained from: