This kit is a Grade 8 Stainless Steel ARP (American Racing Products) bellhousing 1 3/4″ bolt kit for the Buick 401-425 Nailhead engines. They are not only good looking, and don’t rust, but they are super strong for your high horsepower needs and they have a polished finish. These bolts have a tensile strength of 170,000 psi. They have a 1/2 inch 6 point head and a .750 diameter flange for easier access in the tight spots. This kit also includes AN flat and stainless lock washers.