This an exhaust manifold kit for mounting stock manifolds to the heads on your Chevy 409 High Performance 409 H.P. & 425 H.P. V-8 engine. These hex head bolts are ARP Grade 8 stainless and come with a polished finish. These bolts are rated at 170,000 psi. The kit also comes with 1/8 inch thick stainless washers. These bolts are much stronger than the stock bolts. Let us know what H.P. when placing order.