These intake bolts are ARP Grade 8 Stainless steel. This kit fits the stock aluminum intake manifolds. These are not only good looking, and don’t rust, but are super strong for your high horsepower needs and have a polished finish. These bolts have a tensile strength of 170,000 psi. They are 1/4-20 and have a 5/16 inch 6 point wrench head and a .500 diameter flange for easier access in the tight spots. This kit also includes grade 8 stainless bolts and washers for the 2- 3/8-16 thermostat housing bolts and the 1- 5/16-18 distributor hold down bolt. If you have a different intake, or your combination requires different bolt lengths, please call or email us.