Originally Posted by
DiTBho
how confusing it goes ...
Code:
Crown Race Headtube ID Steerer OD Steerer ID
JIS 27.0 30.0 mm 25.4 mm 22.2 mm
French 26.5 .. 27.0 mm 30.2 mm 25.0 mm 22.0 mm
BC1* 26.4 30.2 mm 25.4 mm 22.2 mm
Italian 26.5 .. 27.0 mm 30.2 mm 25.4 mm 22.2 mm
*BC1 = { British, English } referred by Campagnolo
I think the upside from that is you just need an accurate race diameter unless you have French / Italian.
27.0 -> JIS
26.4 -> English (BC1)
When I've bought headsets it always says 26.4 or 27.0 + "did you really want JIS".
Here's the full list of headset sizes:
https://www.sheldonbrown.com/cribsheet-headsets.html
I make that 13 "standards".