Part of the driving harness that is fitted around the horses neck (and chest) and which is connected to the traces, thereby allowing the horse to pull the vehicle (or other object) by leaning into the collar. The most common collars are breast and neck (also called full) collars. The breast collar consists of a wide padded strap that runs across the horse's chest and is held in place by a neck strap. It is buckled directly to the traces (which attach to the vehicle) and is generally used for light carts or carriages.
A neck or full collar is a heavy padded ring (typically made of wood, with a leather covering and wool padding) that is placed over the horse's head an sits at the base of its neck. It may be a closed ring or open at one end (with a bridge of heavy leather). The open ends of the collar should sit on top of the neck, while the rounded end should sit below it. The full collar is connected to the traces and is used for pulling heavier carriages and other items such as agricultural tools, logs etc.