All climbers should own, be trained in using and use personal safety equipment. The two most important pieces of personal gear a climber can own are a helmet and a harness. A climber wears a harness around his waist and legs, and it connects the him to the rope. When the rope becomes taut during a fall, the force generated by the fall is transferred to the harness. Most climbers prefer a comfortable harness with plenty of padding. All harnesses must be sized correctly for proper function. Helmets protect the climber's head not only during a fall, but also from falling rocks and debris. Many of the helmets on the market, like the popular Petzl Ecrin Roc, are unisize, but for a more custom fit, some are sold in size runs.
To absorb the impact from a fall, climb ropes stretch when weighed. This property prevents the climber from suffering injury from the shock and also helps to reduce the force on the rock and the protection used on the climb. Ropes vary in width and length. The most commonly used ropes are 9.8 mm to 10.2 mm (less than a half inch) wide and 60 meters (about 65 yards) in length. Least common are half or twin ropes, which require two ropes to be clipped into each piece of protection. The advantages of half ropes are apparent during rappels, because the climber can descend twice the distance vs. a single rope folded in half. Two ropes also lower the chance the rope system will be severed in a fall over an sharp edge or from rock fall.
Climbers use rock protection to limit the distance of a fall. Starting on the ground as the climber moves up the rock face, he places this gear into the cracks in the rock. When placed correctly, rock protection limits the fall to twice the distance of the amount of rope above the protection. For example, if the climber is 100 feet off the ground, but his last piece of protection is only 5 feet below him, he'll only fall 10 feet---the five feet above the protection and then 5 more feet until the rope becomes taut. Once a piece of protection is placed into the cliff, the climber attaches a carabiner and possibly a second carabiner on a webbing sling, which helps reduce friction of the rope against the rock. Then he clips his rope to the carabiner.
Protection ranges in design from nuts and hexes, which when placed into a constriction in the cliff's crack will statically hold the fall, to tricams and cams, which mechanically increase their hold during a fall. On some climbing, called sport climbs, a prior climber drilled holes into the cliff and placed expansion bolts into the wall. For sport climbs, the climber only needs to carry a set of quick draws, which are two carabiners joined together by a short piece of webbing. To use a draw, the climber clips one carabiner to the bolt and the other to his rope.
When bouldering, the athlete climbs only a short distance off the ground attempting very difficult moves. A boulderer doesn't use ropes, but to protect against the fall, he sets out crash pads. Crash pads are simply big pads that help take away some of the impact from the fall. Often, a spotter, another person who closely watches the climber, will help guide the climber onto the crash pad during a fall by pushing or pulling the climber as he falls.