2.5 Ring Eggbutt
A Ring cheek piece introduces poll pressure as well creating leverage on the mouthpiece, the 2 ½ ring version is the softest version of ring bit as the ½ ring softens the leverage on the mouthpiece and poll.
The Eggbutt cheekpiece prevents pinching of the lips and gives a slightly more solid feel against the side of the face. It also prevents the bit being pulled through the mouth.
The release is slower and also introduces some poll pressure.