ARP Head Studs Subaru EJ Series Phase 2 SOHC - Most Naturally Aspirated SOHC Subaru Models

ARP 99+ Subaru EJ Series Phase 2 SOHC Head Stud Kit

ARP uses a premium grade 8740 alloy that is rated far superior to "aircraft" quality. Then, each stud is placed vertically in special racks and precisely heat-treated to 200,000 psi. 

ARP studs are thread rolled after heat-treat, which gives them about 1000% (that's 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 it's tough on tooling, but the results are well worth the extra effort.