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-lock adjuster, there wasn't a "Poly Lock" on the market that you didnt have to continually tighten. There are several important reasons why ARP's 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 the 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 degree circle. lastly, the set screw is machined flat on the bottom (not pointed) so it will have optimum contact on the rocker arm stud. You'll find ARP perma-loc's 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. Note- ARP Perma-Loc's are designed to be used with ARP's rocker arm studs for best results.