Typically on the H23
The three sheaves at the rear of the boom accommodate the topping lift, which exits at the mast with a couple of feet of tail ending in a stopper knot; the reefing line, which also exits at the gooseneck with sufficient line to allow the sail to be fully raised; and the outhaul. The three jammers at the mast end of the boom allow you to operate the lines from the mast, all in one place. If your boom is empty and you want to run lines, remove the boom from the boat and use a light line with a small weight to go through fist, starting at the mast end. The boom will need to be held almost vertical and wiggled an rolled about to guide the line through. Do it three times, once for each set of sheaves.