XKs Unlimited contracted with the world’s leading manufacturer of high performance engine fasteners to make competition-grade head and main studs. These parts far exceed the strength of original or reproduction fasten- ers and are a must for any high-compression Jaguar engine. The studs are made from 8470 chrome moly with a tensile strength of 190,000psi., the same as used in some NASCAR applications.Standard studs are adequate for a stock engine, but if you’re interested in a high-revving, high-compression Jaguar engine, don’t trust that investment to anything but the best.