23.35 mm for stronglight, 23.3 mm for TA. I've been told you can use a TA remover on Stronglight cranks, but I've also been told you can strip out the threads on a Stronglight crank if you use a TA remover. I'm unsure on which is true, as I have both a TA and a Stronglight remover and always use the approriate one. To tell the two apart if you're unsure, You'd need to (try to) put one in a modern 23mm crank. If they're too big, they're either TA or SL.

Stronglight switched over to a standard threading for crank removers sometime in the late seventies/early eighties.

Note:edited, accidentally put 23mm for a TA remover first time out--should read my own posts once in a while.