Square Taper JIS/ISO

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Square Taper JIS/ISO
Bottom Brackets come in a variety of sizes, types and tapers, each manufacturer clearly specifies which Bottom Bracket type would be compatible with their Chainsets and details are included in the product descriptions on our website so this makes choosing the right BB easy. The manufacturer's guidelines will also provide you with the correct chainline based on a standard rear hub width, so it is important to follow these recommendations in terms of size/type, however you can obviously choose a different brand should this be desirable.

The main issue should be with the thread on your frames BB Shell (where the BB connects to the frame), this will either be BSA (British thread) or Italian thread, BSA is 68mm standard whereas Italian is 70mm but again check the manufacturers guidelines for your frame and product descriptions on our website for the frame bb shell type and bb type.

Are JIS and ISO Taper Bottom Brackets Compatible?

Whilst both versions of the square taper Bottom Bracket look the same, the European made ISO square taper spindles are slightly longer, tapering down to a small end than the Japanese Industry Standard (JIS) Bottom Bracket spindles do.

Obviously this does not affect the actual size of the Bottom Bracket, for example a 107mm ISO Bottom Bracket is still the same length as a 107mm JIS Bottom Bracket and the resultant Chainline will still be the same. You will obviously need to ensure you select the correct size of Bottom Bracket (Width) to obtain the correct Chainline regardless of ISO or JIS status.

If you install an ISO Chainset on a JIS Bottom Bracket decrease your Bottom Bracket width by around 4mm, for example purchase a 103mm BB instead of a 107mm to give you the correct chainline.

If you install a JIS Chainset on an ISO Bottom Bracket increase your Bottom Bracket width by around 4mm, for example purchase a 110mm BB instead of a 107mm to give you the correct chainline.

Most Square Taper Bottom Brackets are ISO nowadays, with JIS only featuring on Miche, Ritchey, Shimano and Sugino Standard (not SG75).

Taper matching was important in the past but all modern day/currently manufactured Chainsets are able to cope with either the ISO or JIS standard taper if they require a square taper bottom bracket, so the products are compatible and work just as well together, just adjust your chainline.