This O-ring is made out of 5/16" diameter material. 2-7/8" Outside diameter against the extra weight in the compactness of the ring allows for a more stable feel and quick release. The mouthpiece is made of 1/2" sweet iron and has three equal breaks. This allows for tongue relief, while intensifying the pressure on the outside of the bars. | Professional's Choice Three Piece O-Ring Snaffle | Size 5-1/4"