A hollow mouth makes this bit lighter and softer whilst the two ring gag offers leverage options to increase severity. The 5" and smaller sizes of this bit have smaller rings to ensure the bit remains in proportion. Mouthpiece thickness: 21mm. Cheek height: 115mm (4.5", 5"), 145mm (5.5", 6"). Stainless steel is the most common material for bits. Durable, easy to clean, tasteless and does not rust