The centre barrel present in nearly all Myler mouthpieces is not a roller but merely a sleeve covering the joint. It protects the tongue from getting caught in the joint; spreads the centre pressure over a wide, smoother area: ensures each half of the mouthpiece is of equal length (unlike a traditional single jointed snaffle); limits the degree of collapse of jointed bits - preventing the nut-cracker action of traditional snaffles; and allows independent side movement.