The ARP Head Studs for the 03-06 Evolution 8 & 9 are constructed of a premium grade 8740 alloy that is rated far superior to aircraft quality. This alloy is heat-treated to 190,000 psi for complete heat penetration. Following heat-treat, each stud is centerless ground to make it as close to perfectly concentric as possible. This procedure involves about ten very slight cuts and results in an exceptionally straight part. Because ARP studs are manufactured to such exacting tolerances, you will note that gaskets and cylinder heads literally glide into position and are perfectly aligned, something that will not happen with inferior quality head studs. ARP studs are thread rolled after heat-treat, which gives them about 1000% (that is ten times) better fatigue strength than those studs that are threaded prior to heat-treat (a very common industry practice).