Duramax 6.6L (2001-2016) Custom Age 625+ARP Head Stud KitDuramax 6. 6L (2001 2016) Custom Age 625+ARP Head Stud Kit With performance enthusiasts adding increasing amounts of turbo boost to diesel applications, ARP has provided an extra measure of security in the form of extra strong head studs manufactured from the firm's proprietary Custom Age 625+ material that has a minimum rating of 260,000 psi tensile strength. They are engineered to provide the clamping force required to keep cylinder heads from