A bolt is an artificial anchor, usually used for building construction, hammered into a hole drilled into rock to protect either a lead climber or for use as a belay and rappel anchor. Most bolts that are used for climbing purposes are construction anchors, either wedge or sleeve bolts that are either 3/8-inch or ½-inch in diameter.
Bolt Use is Controversial
The use of bolts and power drills in climbing is very controversial because it permanently alters and mars the rock surface. The placement of any bolt or the drilling of any hole should only be made by expert climbers that are well aware of both the legal and ethical ramifications of bolting. The placement of a bolt in rock should only be a last resort, and bolts should never be placed next to cracks where other removable protection like nuts and cams can be used, which don’t damage the rock.