Me wearing a curb bit. Note that the bit attaches to bridle via its top rings, and the reins attach to the bottom of the shanks. Photo by cpony.com
Me wearing a curb bit. Note that the bit attaches to bridle via its top rings, and the reins attach to the bottom of the shanks. Photo by cpony.com
Curb bits are, generally, any bits that make use of leverage (i.e. have a lever action). Technically, pelham bits are curb bits, but I consider pelham bits a separate type of bit since they are intended to have the actions of both a curb and a snaffle.
The mouthpiece of a curb bit determines, to a reasonable degree, where and how much (along with the lengths of the shanks) pressure will be applied. With a simple rubber bar used in curb action, pressure will be mostly applied to lower jaw through the tongue and lower teeth (since most human ponies have teeth instead of bars).
A jointed bit will apply more pressure on the pony's teeth (in a bio-equine, this pressure would be applied to the bars).