D-ring bits prevent the bit being pulled through the horse"s mouth.
The anatomically shaped Sweet Iron bits by Waldhausen are bits that have been shaped to the horse"s mouth. Sweet Iron consists of blue steel, when in contact with moisture (in the air), it starts to oxidise and a sweet brown-grey surface rust forms. This stimulates horses" production of saliva. They start to foam up better, which increases the acceptance of the bit.