Originally Posted by
ijsbrand
There are two standards for square tapers: JIS [Japanese] and ISO. The main difference between them is that with JIS the square part is 12.73 millimeter at the beginning, and with ISO it is 12.6 *. So a Shimano crank simply won't shove down far enough on a European taper. And a Stronglight will shove down too far on a JIS square taper.
Still, sometimes that is just what you want.
* some sources say 12.63/12.5
** yes, there have been more sizes in use.
What you really have to watch out for with insertion is taht the taper end will not bottom on the bolt when it's torqued, and that the crank arm is not squished onto the taper base when torqued. The former situation results in the taper not stretching the crank arm properly - the arm will rattle on the taper, and eventually fail the crank after enough cycles of pedaling force. The latter situation will probably overstress the crank arm or the drive side crank. It would also be a failure.