Loose cheek mullen or arched mouth bit.

A LITTLE ABOUT PELHAM AND KIMBLEWICK BITS...

A Pelham Bit combines the actions of a double bridle in one bit. A snaffle rein on the middle ring gives a horse direct pressure to turn or stop, and the second rein (curb rein) is attached to the bottom ring and activates leverage. It is a useful bit for a horse in need of double bridle control but some reason (i.e. insufficient mouth room, tongue too thick) cannot use two bits in their mouth.

A Kimblewick Bit is similar to the Pelham Bit, but with a lower level of leverage.

MULLEN MOUTH BITS - The shaped mouthpiece is very mild and ideal for mouthing young horses.
Sizes - 5 1/2" (13.5cm) 5" (12.5cm) 4 1/2" (11.5cm)