The eggbutt has fixed rings and is therefore stable in a horse's mouth. Because the rings cannot move independently of each other your help will acts directly.
Depending on the type, thickness and material, a eggbutt gets a sharper or softer effect.
The eggbutt is a generally soft basic bit that is reasonably stable in the mouth. The rings cannot move loose from the mouthpiece, so that the help of the hand acts more directly.
Because the rings cannot move independently, no pinching can occur and bit rings are unnecessary.