In rock climbing, a crack climb is a type of climbing route that follows a system of crack(s) or fissure(s) which the climber uses to ascend the route. The width of the crack dictates the techniques needed, and crack-climbs are further differentiated by the body parts that can be 'jammed' into them, such as finger cracks (the narrowest), hand/fist cracks, arm cracks, and body (also called chimney) cracks. Off-width cracks are some of the most awkward, being too wide for the hands or arms, but too narrow to accommodate the body. A top-to-bottom uniform-width crack is known as a splitter crack.
Crack climbing routes require a broad range of techniques, but most importantly emphasize the techniques of 'laybacking' and of 'jamming'. Laybacking requires the crack to be off-set (i.e. one side protrudes) or in a corner, to create the opposing forces needed for the technique. 'Jamming' is where the climber physically "jams" a body-part(s) into the crack which they then pull on to gain upward momentum. The type of rock has an important effect on the effectiveness of 'jamming', with the high-friction surface of granite being particularly suited to the technique. The friction needed for 'jamming' can wear the climber's skin, requiring medical tape or specialist gloves for long crack routes.
