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You CAN fit a ISO crank on a JIS spindle, it’ll just stick out 4 or 5mm more
This is a myth. People assume that because it was on Sheldon Brown, it must be true. It's a pity he didn't live to correct this, because it gets rolled out as fact every time the subject is discussed on any cycling forum, and asserted as an absolute fact by people who have clearly never measured a pile of square taper bottom bracket spindles to see what the difference really is.
Regardless of any JIS/ISO confusion, you should always carefully inspect any square taper assembly, even one which is supposed to be a proper match from the same factory, to ensure that the bolt head doesn't touch the end of the spindle and the crank doesn't touch the runout of the taper at the big end.
gbj_tester-
My Royal H has a modern TA crankset I ran it with a 107 Shimano BB for a few years, I tried it on another bike with much larger chainstays and the the ND side hit the chainstay. When I went to reinstall them on the Royal H I installed them with and 111 Centaur BB and it fits the same.
I also ran a GPM strada cranks on a Shimano BB for about 7 years.
So yeah, I’m not so convinced it’s a myth.
Eeyorecore
You CAN fit a ISO crank on a JIS spindle, it’ll just stick out 4 or 5mm more then the bb measurement. So you’ll never find a JIS spindle short enough for that Crankset.
I’ve been running TA cranks on 107 Shimano BBs for years.