'64 - Smaller bearing hole, bigger bolt holes. '65 up - Bigger bearing, smaller bolts. --Bryan > On Mar 21, 2016, at 1:11 PM, Ed Lindsay via VirtualVairs <virtualvairs at corvair.org> wrote: > > Gathering up cores to take to Helen and I have a question, Clarks is buying 64 only magnesium blower fans - How do you tell the difference ?