I just bought a set of underdrive pulleys from a person on the forum. But it didn't come with bolts so I need to get bolts. While I jack my car up and get under it and I couldn't get one of the bolts off cause my air tool wasn't powerful enought so I found out its a 5/8th. I want and bought three longer 5/8th bolts and when i put them up to the underdrive pulley they are to big for the holes. So what size bolt do I need?

 

I believe the thread is 7/16" unc but the hex head is 5/8".

 

OK that sounds about right cause the auto part store said the stock size was a 7/16th, but the head i know was a 5/8ths.

 

Can I just use a 7/16th bolt and put a washer with it? Will that be strong enought to put on the crank?

 

Better use the same grade bolts. I would say at least a grade 5 bolt, but you can never go wrong with a grade 8.

 

Yeah I would use a grade 8 maybe a dollar more but I would feel much better about it. Should I use a flat washer or a locking washer?

 

If you have an ace hardware, they should have a grade 8 bolt with the flanged head, just like the stock ones. Other wise , I would use a washer.