They're 1/2" coarse thread- - -1/2"-13. 1/2" fine thread is 1/2"-20, and will not engage the block threads. Back in a minute, and I'll give you a measurement.
The short bolts along the manifold would need to be 1/2"X4" to attach a piece of chain and still have a safe thread engagement into the block. The longer ones under the valve cover would need to be 1/2"X6". If the chain is bolted directly to the block without using a piece of angle iron, use a couple of heavy flat washers under each bolt head on top of the chain link.
Jerry
Last edited by Hotrod Lincoln; 06/01/2012 12:53 AM.
