Originally Posted by SkyDog75

JIS (Japanese) and ISO spindles have the same two-degree taper, but the taper runs to a smaller diameter 'point' on ISO spindles. Because of that, a crank arm will sit a few mm farther outboard on a JIS spindle versus an ISO spindle of the same length.

Since you mentioned 'vintage Euro spindles', it might be relevant to point out that there were some other proprietary spindle tapers before just about everyone adopted JIS or ISO.