ARP uses a premium grade 8740 alloy, which is rated far superior to "aircraft" quality, for their Pro Series cylinder head studs. Each stud is placed vertically in special racks and precisely heat-treated to 200,000 psi to ensure complete heat penetration. Then the studs are centerless ground to make them as close to perfectly concentric as possible, unlike lesser quality studs. 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 wont happen with inferior quality head studs. By being thread rolled after heat-treat, these studs have about 1000% (thats ten times) better fatigue strength than those studs that are threaded prior to heat-treat (a very common industry practice). It costs a lot more to do it this way, because its tough on tooling, but the results are well worth the extra effort. This cylinder head stud kit comes complete with premium quality parallel ground washers and conventional hex style nuts.