ring gag

A gag is any item or device placed in or over the mouth during BDSM or sex play to limit its use. Gags make clear speech difficult and muffle other sounds. They can be improvised from things to hand, such as a scarf, a tie, a stocking, rope or tape, or bought as purpose-made gear, which comes in several common styles.

A ring gag is typically a rubber or metal ring placed in the mouth and secured with straps. This keeps the wearer's mouth open and accessible for insertion of objects.