Because of its jointed mouthpiece the Tom Thumb Bit is often mistakenly called a snaffle. It is actually a curb bit with a jointed mouthpiece and swivel shanks. The combination of the jointed mouthpiece, leveraged rein attachment, and curb can make the Tom Thumb a very severe bit. It is so powerful (the name "Tom Thumb" being derived from the name of an early locomotive) that some heavy-handed riders have even broken their horse's jaw with it.
Photo by Bob Lemen. All rights reserved.