Just to close the loop, they are indeed 7/16-20. I think that changed in '67 or '68, as I have some other bolts from a Corvair that are 1/2" coarse thread. --Bryan On Sep 10, 2013, at 10:37 PM, Bryan Blackwell wrote: > Hi folks, > > Can someone tell me the size (diameter and thread pitch) for the stock seat belt bolts in a '66? > > --Bryan