The Eggbutt chhekpiece prevents pinching of the lips and gives a solid feel against the side of the face. It also prevents the bit being pulled through the mouth. The release is slower than the loose ring and also introduces a light poll pressure.
There are 2 products.
2906 Myler 06 Low Ported Mullen Barrel Snaffle on a Plain Eggbutt cheek
2933 Myler 33 Ported Barrel Snaffle on a Plain Eggbutt cheek