For pulling heavy loads, a full collar is required because it distributes pressure over a larger area of the horse.
Attaching the harness to the vehicle or load is called putting to in the British Isles,[1]: 219 or hitching in North America.
[2]: 305 A painting on a lacquerware box from the State of Chu, dated to the 4th century BC, shows the first known use of a yoke placed across a horses's chest, with traces connecting to the chariot shaft.
[2]: 310 The hard yoke across the horse's chest was gradually replaced by a breast strap, which was often depicted in carved reliefs and stamped bricks of tombs from the Han Dynasty (202 BC – 220 AD).
Traces are the two straps or chains which take the pull from the breast collar or hames to the vehicle or load.
They usually include blinders, also called blinkers or winkers, beside a horse's eyes to prevent it from being distracted or frightened by the carriage or other activity behind or beside it.
Often there is ornamentation on the bridle such as a drop hanging from the crownpiece and down the forehead, rosettes on each side by the ears, and decoration across the browband.
[1]: 25–7 [3]: 89–90 Reins or lines are long leather straps (occasionally ropes) running from the bit to the driver's hands which are used to guide the horses.
In English carriage harness, a bearing rein or side check travels through rings near the horse's ears and attaches to the bit.
Properly adjusted bearing reins and overchecks give the horse ample freedom of his head while prohibiting a horse from reaching to eat grass or scratching sweaty bridles on anything within reach—potentially causing accidents when a bit or rein gets hooked on something.
The middle section of a harness includes the parts that go around the horse's mid-section and hold shafts.
Saddles for heavy commercial carts may be quite substantial in size to help distribute the weight bearing down from the shafts.
Two types: A strap going through the harness saddle, or attached to it, to join the belly band on both sides of the horse.
It prevents the shafts from rising up, especially on a two-wheeled vehicle where weight on the rear of the cart may tip the front up.
Called "false", because unlike a true martingale it does not attach to the bridle or have any influence on the horse's action.
Terrets are mounted on the saddle or collar to support the reins and keep them in position.
[1]: 229, 272 The purpose of the rear section of harness is for holding the traces (the pulling straps) up off the ground so a horse doesn't get a leg over one, and for the horse to slow or stop a wheeled vehicle, or "hold back" the vehicle against gravity when going downhill.
Similar to wagon harness but without breeching, used for dragged loads such as plows, harrows, canal boats or logs.
The New England D-Ring makes use of a metal D-shaped ring that allows for a ninety degree angle to be maintained at the junction of the front trace and the hames regardless of the height of the implement being pulled.
The Western harness does not provide this flexibility but has other useful characteristics such as a strap that runs from the breeching to the collar which stops the pull from riding up and hitting the horses in the face when descending a steep incline.