One of the more aggravating things found in many high performance engines is constantly having to re-adjust rocker arms. Until ARP introduced the patented Perma-Loc adjuster, there wasnt a poly lock on the market that you didnt have to continually tighten. There are several important reasons why ARPs exclusive Perma-Loc rocker arm adjusters wont loosen like others. First, the adjuster body is heat-treated all the way through (not just case hardened). This eliminates the thread movement common to others. Secondly, the threads are machined exactly perpendicular to the bottom of the adjuster, so it seats evenly and applies pressure on a full 360 circle. Lastly, the set screw is machined flush on the bottom (not pointed) so it will have optimum contact on the rocker arm stud.Youll find ARP Perma-Locs easy to use, too. The compact 12-point head is designed to hold your wrench in position while you lock the set screw with an Allen wrench. Features 12-point head with special shouldered stop to hold wrench. Eliminates need for special adjusting tools. Forged in-house from 8740 alloy chrome moly steel and heat- treated throughout (not simply case hardened, as others are). Bottom flush-ground perpendicular to threads. Threads are precision CNC-machined exactly perpendicular to the bottom of adjuster to ensure an optimum seat and even pressure. Set screw has flush-machined tip for optimum contact and seating on stud. Threads machined for maximum engagement. Stud Girdle 16Pieces Body 1.200/1.485 Diamater .750 Length 2.050/2.615 Shank .600 Thread 7/16-20