This photograph shows a kimberwick bit in the correct position in a horse's mouth. The Kimberwick is a horse bit with D-shaped rings on either side of the horse's mouth. The "D" ring is offset, so the mouthpiece is on the upper part of the flat side of the D, and the kimberwicke is used with a curb chain. The kimberwick has a curb effect, which applies pressure not only in the mouth but at the poll (top of head behind ears) and under the jaw where the chain rests. The pelham bit is used with a single rein, but can be used with two, one in either slot.
The Uxeter kimberwick, the most common kimberwick, has slots in the curved portion of the D, so that the rein is fixed. This increases the curb effect, especially when the rein is placed on the lower of the two slots.