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 rocker arm adjuster, there wasn't a "poly lock" on the market that you didn't have to continually tighten. There are several important reasons why ARP's exclusive Perma-Loc rocker arm adjusters won't loosen like others. First, the adjuster body is heat treated all the way through (not simply case hardened), which eliminates the thread "movement" common to others. Secondly, the threads are machined exactly perpendicular to he bottom of the adjuster, so it seats evenly and applies pressure on a full 360 degree circle. Lastly, the set screw is machined flush on the bottom, not pointed, so it will have optimum contact on the rocker arm stud. Perma-Loc adjusters are also easy to use, because the compact 12-point head is designed to hold your wrench in position while you lock the set screw with an Allen wrench.