ARP Head Studs Stud Kit for SUBARU WRX & STI 2.0L 2.5L TURBO EJ205 EJ255 EJ257. That’s why ARP head studs are popular among leading Sport Compact/Import racers. You should know that ARP uses a premium grade 8740 alloy that is rated far superior to “aircraft” quality. Then, each stud is precisely heat-treated to 200,000 psi. Following heattreat, 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. It’s important to note that lesser quality studs are not even centerless ground-the material is thread rolled in bar stock form (mostly before heat-treat, when the material is easier to machine). 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 won’t happen with inferior quality head studs. 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. Prevent blown head gaskets and ensure optimum sealing! ARP HSK Subaru WRX STI EJ20 EJ25. We accept all major credit cards. Head Bolt Set for Ford 5.0L 302 V8 OHV – HB106 – 2 Sets Required. HBK142 Head Bolts Set for Chevrolet GM SBC 283 327 305 350 5.7 5.0. Complete Head Bolts Set for 2003+ Chrysler Dodge Jeep Hemi 5.7 6.1 6.4 Engines.