ARP head stud bolts  VW 2.8/2.9L 12v VR6 U/C U/C is an abbreviation for "Undercut", which means that the bolts have a slightly smaller diameter on the unthreaded part of the bolt. The undercut improves the tightening of the cylinder head more evenly compared to those that are not undercut as they stretch. This can be an advantage if, for example, the cylinder head gasket would not be 100% smooth over the entire surface, then the bolts compensate for this. Socket size: 1/2 12pt, 3/16 Allen Thread : M11x1.5 Tightening torque:  Tightened in 3 steps. Step 1: 25 ft/lbs Or 33.9 nm Step 2: 50 ft/lbs Or 67.8 nm Step 3: 80 ft/lbs Or 108.4 nm Assembly instructions