1. Rein ring: terret – One of the metal rings on the top of the harness saddle, through which the reins pass.A terret or rein ring is a metal loop on a horse harness through which the lines (reins) pass to prevent them from tangling or getting snagged on the harness or shafts.The lines run from the hands of the driver, through the terrets, and then attach to the horse's bit to...