recently had to get me some crank bolts for my M952 BB.
they take M15 guaranteed, i bought some Ti self extractors from toronto cycles.
the above picture is of some self extractors. the black part which is seperate from the silver part is not essential to be able to fit and ride the cranks.
as has already been said 99% of the time it just sits and makes the cranks look pretty.
as long as the bolt is an M15 that is all you really need.