XKs recently contracted with the worlds 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 fasteners 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 youre interested in a high-revving, high-compression Jaguar engine, dont trust that investment to anything but the best. This kit will not show as being in stock but no worries; it is assembled from individual pieces when ordered.