ARP's Perma-Loc Rocker Arm Adjusters are a true 'poly lock' that you wont have to continuously tighten. These rocker arm adjuster are heat-treated all the way through, eliminating the thread “movement” that is common to other adjusters. The threads are machined exactly perpendicular to the bottom of the adjuster, so they seat evenly and applies pressure on a full 360° circle. Set screws are machined flush on the bottom (not pointed) so they will have optimum contact on the rocker arm stud. A compact 12-point head is designed to hold your wrench in position while you lock the set screw with an Allen wrench.