Type of bit which has lever arms or shanks with fixed rings above the mouthpiece to which the cheekpieces are attached and rings at the bottom of the shank to which a pair of reins is attached. Due to the lever action of the shanks, the action of tightening the reins applies pressure to the poll and if fitted with a curb chain also to the lower jaw (the horse's 'chin' region). The actual mouthpiece of the curb can be a bar, or may have a single or double joint. It is typically used together with a second bit (a bradoon bit) which is very similar to a snaffle in style but tends to be smaller. These bits are used with a double bridle.