Cycle Engineers' Institute (CEI)
screw thread

Replaced by the British Standard Cycle thread series.

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
13	0.092	62	49
12	0.104	44	47
—	1/8	40	2.5 mm
	0.154	40	30
	5/32	32
	0.175	32	27
	3/16	32	23
	7/32	26
	¼	26	4
	17/64	26
	9/32	26
	5/16	26	1
	3/8	26	8.5 mm
	7/16	26
	0.4724 (12 mm)	26
	½	26
	0.5512 (14 mm)	26
	9/16	26 +20?	13 mm
	5/8
	0.9675	30
	1	26	24.5 mm
	1.29	24LH	1¼
	1.37	24	1 21/64
	1 7/16	24LH	35.5 mm
	1½	24	37 mm