Completely wrapped in high-quality scaled polyurethane, the O-ring bit is rigid yet gentle on the teeth. The strap, also made from durable PU, has a completely adjustable 15 hole fastening to suit all subs. The O-ring has an inner diameter of 3.2cm (1.3'') and sits behind the teeth leaving the mouth and jaw invitingly open. The strap has a total length of 67.5cm (27'') including O-ring and is 4.4cm (1.8'') wide.