Shimano 105 cranks have a few different model depending on year. The exact model # should be stamped on the back next to the pedal attachment hole. Looks something like "FC-1056" (if 1992 original crank). Let us know the model # and someone will probably know the bottom bracket length & spindle interface. Most 105 doubles use a 130 BCD and takes a 39t small ring (38t on some generics) minimum since the chainring bolts would not allow any smaller.