Action: The loose ring is a circular ring which may rotate around on the mouthpiece. The sliding makes it more difficult for the horse to tighten against it, promoting relaxation and chewing from the horse. The loose ring therefore keeps the bit more mobile than any other ring type. The ring will also rotate slightly before the bit mouthpiece adds pressure to the mouth, thus allowing it to give more signal than a more fixed bit. Disadvantages: the loose ring may pinch the corners of the lips as it rotates, causing pain to the horse. This is especially a problem if the bit mouthpiece is too small. If this occurs, a bit guard may be used. The bit mouthpiece should be slightly wider (to accommodate the bit guard) should one be used; it is best if it is at least 1/2 inch wider than required by the horse's mouth. There are some horses that dislike the rattling noise of the loose ring. Additionally, the loose-ring is more easily pulled through the mouth than a bit with cheeks.
Dee-ring/ Racing snaffle
Pinchless Dee-ring variation with decorative conchos added
Types of Bits: snaffle. The kimberwicke shank has a modified Dee-ring design. Action: the Dee-ring, as its name suggest, has a ring shape like a "D" with the cheek side of the "D" attached to the mouthpiece of the bit. The straight bars of the Dee-ring provide a slight lateral guiding effect. This is because the bit ring is pulled against the side of the mouth opposite the rein that is activated, pushing the sides of the Dee against the horse's mouth, encouraging a turn. The Dee-ring is fixed in the horse's mouth, because its shape does not allow the bit to rotate. The Dee-ring is most similar to the full cheek. Advantages: does not pinch like the loose ring, and is not as likely to be pulled through the mouth as a loose ring or eggbutt. Otherwise is fairly mild, but acts quickly on the mouth of the horse. Disadvantages: Has little loose movement and thus provides less warning to the horse.
I personally prefer the D-ring snaffle but I have read in a great book (will try to remember to come back here to post the title) that some judges prefer to see horses in regular snaffle bits such as these over pelhams etc as it shows the horse is a lot more sensitive and souple to the rider's aids.
I could see how that would be. Tho we all ahev different views on him, I believe it was one of the books written by George Morris.