ARP 1544005 Pro Series Cylinder Head Studs with Hex Nuts The choice of many top professional engine builders for their all-out competition powerplants Manufactured from a premium grade 8740 alloy that is heat-treated to 200,000 psi, which is considerably stronger than Grade 8 hardware Kit comes complete with premium quality parallel ground washers and conventional hex style nuts 1000% better fatigue strength than many other studs Centerless ground to be as perfectly concentric as possible