Thanks Ed. I'll verify the threads this weekend.
When I was researching the 3866568 stud, I found some info about the threads being 3/8"-16.
This is what a place called Pontiac Paradise has to say about it:http://pontiacparadise.com/shoptalk/2011/01/
They also have an ebay auction with similar info:http://www.ebay.com/itm/NEW-Reproduction-GM-Ball-Stud-used-60s-70s-GM-/250759330161?hash=item3a626bb971&item=250759330161&pt=Vintage_Car_Truck_Parts_Accessories&vxp=mtr
I also found some posts on Team Camaro about the threads being 3/8"-16. You can't always believe what you read or see in the internet, so I wanted to be sure. I'm fairly sure the threads on the one I have are 1/2"-13.