British Tools & Fasteners - CEI Thread Profile

This thread series was superseded by BSC (British Standard Cycle) thread. The Thread Profiles were kept, but some of the less popular sizes were dropped

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Cycle Engineers' Institute (CEI) or British Standard Cycle (BSC)

These are different names commonly used for the same threads. 60 degree thread angle, rather than the 55 degree of BSW and BSF. For sizes from 1/4" through 1/2" by far the most common are 26 tpi, although 24 tpi appear as well. Most, but by no means all, fasteners on post-War BSA's (through the late '60's, when it got more complicated) were CEI. Although the thread form and pitch is different, the head sizes on CBI-threaded fasteners use the same wrenches as BSW/BSF.

Size (inches)	Wire Gauge	Threads per inch	Pitch	Core Diameter	Usual Applications	Tapping Drill Size
0.056 inch	17 WG	62 Tpi	0.0161 ins	0.0388 ins	Spokes	Number drill 61 1mm 0.0394 inch
0.064 inch	16 WG	62 Tpi	0.0161 ins	0.0468 ins	Spokes	0.0469 inch (3/64)
0.072 inch	15 WG	62 Tpi	0.0161 ins	0.0598 ins	Spokes	Number Drill 54 0.0551 inch 1.4mm
0.080 inch	14 WG	62 Tpi	0.0161 ins	0.0628 ins	Spokes	Number Drill 52 0.0635 inch 1.6 mm
0.092 inch	13 WG	56 Tpi	0.0178 ins	0.0729 ins	Spokes	Number Drill 49 0.0728 inch 1.85mm
0.104 inch	12 WG	44 Tpi	0.0227 ins	0.0798 ins	Spokes	Number Drill 46 0.0807 inch 2.05mm
0.125 (1/8th) inch	_	40 Tpi	0.025 ins	0.0984 ins	Small Fixing Screws	Number Drill 39 0.1004 inch 2.5mm
0.154 inch	_	40 Tpi	0.025 ins	0.1274 ins	Chain Couplings	Number Drill 30 0.126 inch 3.25mm
0.175 inch	_	32 Tpi	0.0312 ins	0.1417 ins	General Use	Number Drill 27 0.126 inch 3.25mm
0.1875 (3/16) inch	_	32 Tpi	0.0312 ins	0.1542 ins	Misc Screws	Number Drill 23 0.1562 inch 3.97mm
0.250 (1/4) inch	_	26 Tpi	0.0385 ins	0.2091 ins	Crank Cotters	Number Drill 3 0.2188 inch 5.56mm
0.266 inch	_	26 Tpi	0.0385 ins	0.2280 ins	General Use	Number Drill 1 0.2283 inch 5.8 mm
0.281 inch	_	26 Tpi	0.0385 ins	_ ins	_	Letter Drill D 0.2441 inch 6.2 mm
0.3125 (5/16) inch	_	26 Tpi	0.0385 ins	0.2715 ins	Front Wheel Spindles	Letter Drill J 0.2756 inch 7 mm
0.5625 (9/16) inch	_	20 Tpi	0.05 ins	0.498 ins	Pedal Pins in RH and LH Thread	0.5156 (33/64) inch 13.1 mm
0.9675 (9/16) inch	_	30 Tpi	0.033 ins	0.954 ins	Steering Stems	_
1 inch	_	26 Tpi	0.0385 ins	0.959 ins	Steering Stems	0.9688 (31/32) inch 24.61.1 mm

CEI (Cycle Engineers Institute) Thread Data