This an exhaust manifold kit for mounting stock manifolds to the heads on your big block Chevy V-8 engine. The bolts and 1/8 inch thick washers are 304 stainless steel and the bolts are 1 1/4 inches long. They are for the engines that use all 3/8 bolts in the heads. Please verify the fit to your engine before ordering. These bolts are not as strong as the stock bolts.