The actuator arm is a "T" shape with a small hook formed at the bottom of the "T". (Fig. 4a) I bent these from .045-.048 guitar string. The cross bar of the "T" is shorter than the width (front to back) of the PC material, and it droops down a bit on one side to hook over the pivot point. The bottom leg of the "T" reaches from the right hand pivot to the center of the coupler pocket, with the center of the hook loop directly over the mounting screw. (Fig 5-A) Form it this way: Cross the top of the "T" from left to right. Bend a "U" in the end (Fig 4-E) for the return spring, (Fig 5-C) and then back across the top to just past center. Then turn a right angle down around the pivot point to near the end. Finally make an almost closed loop for the chain. The loop should center over the mounting screw. (but clear it) This allows the coupler to swing with no change in the length of the chain.