British Standard Cycle (BSC or BSCy or CEI) is a British Imperial screw thread standard. Unlike other major British imperial thread standards (

British Standard Whitworth British Standard Whitworth (BSW) is a screw thread standard that uses imperial-unit, imperial (inch-based) units. It was devised and specified by British engineerJoseph Whitworth in 1841, making it the world’s first national screw thread stand ...

and British Standard Fine) the thread runs at a 60 degrees rather than a 55 degrees

angle In Euclidean geometry, an angle can refer to a number of concepts relating to the intersection of two straight Line (geometry), lines at a Point (geometry), point. Formally, an angle is a figure lying in a Euclidean plane, plane formed by two R ...

. All sizes inch and larger use 26

threads per inch A screw thread is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a ''straight'' thread and th ...

(tpi), making them similar to 1 mm ISO threads, which are 25.4 per inch and also run at a 60 degrees angle. It was originally used with both

bicycle A bicycle, also called a pedal cycle, bike, push-bike or cycle, is a human-powered transport, human-powered or motorized bicycle, motor-assisted, bicycle pedal, pedal-driven, single-track vehicle, with two bicycle wheel, wheels attached to a ...

s and

motorcycle A motorcycle (motorbike, bike; uni (if one-wheeled); trike (if three-wheeled); quad (if four-wheeled)) is a lightweight private 1-to-2 passenger personal motor vehicle Steering, steered by a Motorcycle handlebar, handlebar from a saddle-style ...

s. However it is now believed to be obsolete in motorcycle manufacture. In the bicycle industry it is still found on virtually all bottom bracket threads and the wheel axles of low-end models manufactured in China, which are derived from pre-WWII British roadsters. BS 811: 1950 provides specifications for British standard cycle threads. Cycle thread in and inch sizes also come in 20 tpi and 24 tpi options. 1/4" diameter cycle thread nuts and bolts have the same 26tpi as 1/4" BSF, which means that they will fit each other in this diameter only. Traditionally the parts it would be found on are: * Front axle and seat pin clamp bolt diameter, 24 or 26 tpi threading * Rear axle diameter, 26 tpi * GB Stems using diameter, 26 tpi for the handlebar clamp Note that M8 × 1.00 metric threaded parts can interchange with diameter × 26 tpi parts with a " Class B fit", meaning you should not go back and forth between threadings. British Bicycle standards for other parts which are not strictly BSC but come in similar fine threads include: * Bottom Bracket cups diameter with a 24 tpi ISO standard or a 26 tpi

Raleigh Raleigh ( ) is the List of capitals in the United States, capital city of the U.S. state of North Carolina. It is the List of municipalities in North Carolina, second-most populous city in the state (after Charlotte, North Carolina, Charlotte) ...

(now obsolete) standard

History

The thread was defined to meet a requirement for a thread form for

s and

s, originally specified by the Cycle Engineering Institute. Before being adopted as a British Standard it was known as the CEI thread.

References

Thread standards Screws British Standards {{standard-stub

History

See also

References