Mullen Mouth Eggbutt Bit Flat Ring The Eggbutt bit is mild and won't pinch the horse's lips. The mouth piece does not rotate around the ring. This bit features 3 inch rings and a 10 mm mouth. All our Bits are High Quality German or Stainless Steel made by Coronet or Korsteel. Size: 4, 4 1/2, 5, 5 1/2.