An eggbutt or Cheltenham gag looks like a regular eggbutt snaffle, except that holes are bored into the top and bottom of the cheeks, allowing a rein to pass vertically through the rings. This type of bit combines the strong squeezing action of the over-cheek rein with the increased lateral control of the eggbutt cheek piece.

Because the action of a gag can be very strong, it is fairly easy to end up pulling the bit through the horse’s mouth, so the eggbutt shape resists that and transfers some of the pressure to the opposite side of the mouth.