Originally Posted by upnover
"snaffle" is the overall name for a bit that has a single joint and acts on the bars of the horse's mouth. "full cheek" describes the sides of it. I think full cheeks help turn a horse easier because it actually turns the nose a bit and you don't have a ring that's going to slide through your horse's mouth. I use a rubber bit guard (a flat round circle of rubber with a hole in the middle) on my loose rings to keep that from happening! With a D ring you shouldn't have that problem (the d should act very similarly to the full cheek) but you could try the bit guards. They're only $2 or 3.
Nope. A snaffle can have ANY kind of mouthpiece, not just a single joint. The term just refers to a bit that works off direct pressure I.e. No leverage/no shanks.
A full-cheek is often used for young horses as it reinforces the turning aid. I'm not a fan of bit guards, but we have used a full cheek (also called a fulmer) smaffle on one of our ponies as she had a nasty habit of gaping her mouth open to allow the bit to slip through and avoid the turn. A D-ring SHOULD solve this, as this is what the flat side of the rings is designed for, unless the horse is really gaping its mouth. If that's the case you might want to invest in a full-cheek until you can get that problem sorted.