Shaft tugs, or simply "tugs," are leather straps of loops that attach to the back of a horse's or other working animal's harness, connecting the horse's tack to the vehicle it pulls. Tugs transfer the force of the movement from the harness to the saddle, then to the cart, carriage, plough or other vehicle. There are three primary types of tugs designed for different pulling situations.
English tugs are used with two-wheeled vehicles that have straight shafts. These tugs allow the cart's shafts to rise and move with inclines the horse may encounter. By letting the shafts "float," the passengers have a relatively smooth experience as the horse grapples with hills or dips. If a tighter fit is needed, additional wrapping, called a "wrap girth" or "shaft wrap" can be used with English tugs to hold the cart shafts down and move the vehicle with the horse and the terrain.
French tugs are also used for two-wheeled vehicles, but only when the cart's shafts have an upward curve. French tugs are considered somewhat ornate in the horse carriage world, but are also a practical choice when the shafts need some additional force to hold them down and keep the cart stable, as when using English tugs in tandem with shaft wraps.
Tilbury tugs are for four-wheeled vehicles. Tilbury tugs are, like French tugs, designed to buckle tight around the shafts of the vehicle, so the cart and horse move as one. As a matter of safety, Tilbury tugs are never to be used on two-wheeled vehicles.