Neat Plastic Hook
I use these on the end of dinghy 4mm halyard tails:
a) tension the tail by hooking onto some elastic e.g. toestrap bungees when ashore on the berth. Stops that annoying clatter of loose halyards against the mast! And...
b) the hook also acts as a stopper knot so you don't risk losing the be end of your halyard up the mast!