Looking for lower alternator bolt for 1965 skylark with 300. The bolt measures 6-1/2" including the head.
You may want to check, Oldsmobile, Pontiac, and Chevrolet website you may get lucky and find one that’s close or you may find the correct one.
3/8" - 16 coarse thread?? If you said 6 1/4" long, including the head, that's a 3/8" - 16 - 6 inch bolt. Should be commonly available - at lowes, home depot, etc. I'd be happy to send you one, used, grade 5, if I have it. PM if interested.
