British Standard Cycle

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British Standard Cycle (BSC or BSCy) is a British Imperial screw thread standard. Unlike other major British imperial thread standards (British Standard Whitworth and British Standard Fine) the thread runs at a 60 degrees rather than a 55 degrees angle. All sizes 14 inch and larger use 26 threads per inch (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 bicycles and motorcycles. [1] However it is now believed[ by whom? ] 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.[ citation needed ]

British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard.

British Standard Fine (BSF) is a screw thread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread. It was used for steel bolts and nuts on much British machinery, including cars, prior to adoption of Unified, and later Metric, standards. For highly stressed conditions, especially in motorcycles, a finer thread, British Standard Cycle (BSC), was used as well.

Degree (angle) angle unit; π/180 radians

A degree, usually denoted by °, is a measurement of a plane angle, defined so that a full rotation is 360 degrees.


Cycle thread in 716 and 12 inch sizes also come in 20 tpi and 24 tpi options.

Traditionally the parts it would be found on are:

Note that M8 × 1.00 metric threaded parts can interchange with 516 inch (7.94 mm) 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:


The thread was defined to meet a requirement for a thread form for bicycles and motorcycles, originally specified by the Cycle Engineering Institute. Before being adopted as a British Standard it was known as the CEI thread.

Bicycle Pedal-driven two-wheel vehicle

A bicycle, also called a cycle or bike, is a human-powered or motor-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A bicycle rider is called a cyclist, or bicyclist.

Motorcycle Two- or three-wheeled motor vehicle

A motorcycle, often called a bike, motorbike, or cycle, is a two- or three-wheeled motor vehicle. Motorcycle design varies greatly to suit a range of different purposes: long distance travel, commuting, cruising, sport including racing, and off-road riding. Motorcycling is riding a motorcycle and related social activity such as joining a motorcycle club and attending motorcycle rallies.

See also

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Outline of bicycles Overview of and topical guide to bicycles

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  1. Morgan, Brian. "BSC (British Standard Cycle) Thread Data" . Retrieved 2017-04-26.