Eggbutt Lock Up from Bombers.

The Eggbutt prevents the horse from being pinched in the lips/corners of the mouth by the bit rings and provides a more stable feeling in the horse's mouth. It also prevents the bit from sliding through the mouth. The release is somewhat slower, and it also applies a little pressure on the neck. The Lock Up mouthpiece prevents the nutcracker effect of regular jointed bits, which reduces pressure on the bars. Therefore, Lock Up is milder than a regular jointed bit, but it still applies pressure on the tongue and bars when the reins are shortened.