Eggbett Lock Up from Bombers.

The eggbutt bit prevents the horse from being pinched at the lips/corners of the mouth by the bit rings and provides a more stable feel against the horse. The eggbutt bit ensures the bit stays still in the horse's mouth.
The Lock Up mouthpiece prevents the nutcracker effect of regular jointed bits, which reduces pressure on the bars. Lock Up is therefore milder than a regular jointed bit, but it still applies pressure to the tongue and bars when the reins are shortened.