This is the headboard on a Santa Cruz 52 mainsail. In real life it is 8.25 inches across the top edge. There are two aluminum plates rivited through the head of the sail.

Since this is a fairly large boat, notice that there are two small cheek blocks bloted onto the headboard. These are used to route the leech cord across the head and down the luff. The cleats for the leech cord are at the cunningham and reef tack rings. With this arrangement, when you tighten or loosen the cunningham, you also are tightening or loosening the leech cord at the same time.