Campag vintage cranks & mtb pedals

was trying to put on a set of shimano mtb pedals and relised that they were very hard to wind into the campag crank arms, so i stopped amd looked at the thread on the old campag pedals compared to the shimano mtb pedals and they looked identical?? i greased up the thread before trying to put them in but still had too much resistance for my liking :? anyone had this issue or knows if there is a difference in thread size for these old cranks???

press the threas together from the old pedals to the new. if they interlock then they have the same thread. if they dont, then dont try and screw them in.
Threads can be deceptive esp the pitch, thats a simple way to check

There are thread tolerances, which might be the wrong way for your combination of cranks (too small) and pedals (too large) or there might be dirt in the threads. It is possible that the cranks are Italian thread and the pedals are English thread, similar but a different thread angle (55 vs 60 degrees but same thread pitch). Run pedal taps through the cranks to make sure everything matches.