Reins are among the most easily recognisable pieces of tack -- equipment for riding a horse -- a rider uses. As the phrases "rein in" or "free rein" indicate, reins are a mechanism used to control the horse's movement. Attached to the bridle, reins are used by the rider to change a horse's direction or indicate it should stop. Basic structure is generally long leather straps attached to the bridle on either side of the horse's head.
Closed & Split Reins
Closed and split reins are the most common types of reins for horses; most other types are derivatives of these two types. Closed or loop reins are made from a single piece of material -- usually leather -- that runs from one bridle loop to the other, behind the horse's neck and is then grasped by the rider. This single-piece construction makes it easier to hold onto and is common for English riders. Split reins are two-piece reins; one piece loops to one bridle loop and each rein is then held by the rider. The split design keeps the horse from getting his feet tangled in the rein loop, which is more likely to occur with closed reins.
Draw & Running Reins
Draw and running reins vary from standard reins, which run from the bridle to the rider's hands. Instead, they are attached to the saddle, thread through the bridle loop and then back to the rider. Due to this unusual pattern, the reins themselves are long. This style of reins offers the rider more control over the horse's movements.
Side, Long, & Driving Reins
Side, long and driving reins are not meant to be held by a rider. Side reins are used most often in training; they connect from the bit to the saddle. Similarly, long and driving reins attach at the side; they are used to handle the horse from the ground or a cart.
Curb, Snaffle & Double Reins
Curb and snaffle reins are used with double bridles or Pelham bits; they feature two reins on each side of the horse's head. Snaffle reins are laced together; curb reins are buckled. Double reins feature both a snaffle and a curb rein, attached to a double bridle.
Mecate & Romel Reins
Romel reins originated with the vaqueros -- Spanish cowboys. Most often used by Western riders, they are a type of closed rein that also features a whip, or "quirt." Mecate reins are used with bitless bridles; instead of being made of leather, as most reins are, they are composed of a single piece of rope that forms a closed rein. Mecate reins are often accompanied by lead reins, an extra piece of rein.