The eggbutt snaffle has fixed side pieces so the ring cannot move. It works on lips, corners of mouth, bars and tongue. The fixed bit however prevent possible pinching.
The loose ring works on the same parts of the mouth, but you give the horse more opportunity to play with the bit.
I ride in a double jointed loose ring, he goes better in the loose ring than in the eggbutt as he can play with it and also the double joint prevents the nutcracker effect.
Hope this helps, I am no expert at all, maybe someone else can explain it better than me.
Loose ring are as described! The mouth piece has holes at either end thru which the rings of the mouthpiece fit, this causes a bit that will always have some movement as the rings will be moving thru the mouthpiece as the horse is ridden. The eggbutt's rings are 'sealed' onto the mouthpiece, the rings stay stable as the horse is ridden and the mouth stays alittle stiller.
Loose rings= allow for movement, play, poss for a fussy horse who likes to mouth the bit, youngsters.
Eggbutts= still rings keep the bit still, good riding school bit! good for horses who fuss on a moving bit who like stability.
ooh!that was really academic of me !