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CEI (Cycle Engineers Institute) Thread Data

This thread series was superseded by BSC (British Standard Cycle) thread.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

No Thread Profile Drawing Available

Angle of thread = 60 o.

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

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