Belt eh?

A reef tackle is a piece of thick cord put through a reinforced hole in a sail.

To reef the sail it is folded up or down - depending on if square or fore and aft rigged - onto the spar it is attached to, then the two ends of the reef tackle are knotted together (in a reef knot)around the folded sail and spar. There would be a line of them all along the sail at the same level, to shorten the sail.

There would be binding at the end to stop it unlaying, and is usually a double knot each side at the top to stop it pulling through the sail - at the top of the dangly bit - do I need to draw you a picture?