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Japanese Industrial Standard (J.I.S.)
From WikiPedalia
Less-expensive Japanese bicycles use J.I.S. sized headsets, better ones use Campagnolo-sized headsets. Frames and forks built for J.I.S. headsets can be machined to fit standard Campagnolo-type headsets.
J.I.S. fork crown seats are 27 mm in diameter, instead of 26.4 mm
J.I.S. head tube inside diameter is 30 mm, instead of 30.2mm
J.I.S. square-taper bottom-bracket axles use a marking system which is consistent across numerous brands.
