ARP's Undercut Head Studs are manufactured from premium 8740 chrome moly steel and heat treated to 190,000 psi. These studs are thread rolled after the heat treating process, which vastly improves their fatigue tolerance. Undercutting of the stud equalizes the "stretch", which makes for a more consistent clamping force; and one that compensates for head gasket compression when the cylinder heads are installed. This helps prevent blown head gaskets, and assures optimum engine sealing. Included are 12-point nuts and parallel ground washers.
https://www.ebsracing.com/FeauredProducts/ARP/ARP-Porsche-Head-Stud-Kit/ARP-204-4206
Head studs hold your head and block together. As you make more power than your engine was designed to hold from the factory, the head and the block push apart from each other, stretching the factory bolts and causing various failures. ARP Head Studs are stronger than the factory ...