Diameter too small or length too short? For the latter, you will find that longer pins are extremely difficult to work with. As it is, I've found you have to insert the pin until it hits the recess the nut is in, then turn the bolt until you can continue pushing the pin home. At least one bolt on my engine is awkwardly placed so that I can't align it so that a pin will have no interference on both sides, so the called-for pins are the best I can do. It can also be a real pain to turn the pin ends over in some of the hard-to reach spots.