Spring loaded camming device
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A spring loaded camming device (also SLCD or just cam) is a piece of rock climbing or mountaineering protection equipment. It consists of two, three, or four cams mounted on a common axle or two adjacent axles, so that pulling on the axle forces the cams to spread further apart. The SLCD is used by pushing on the cam via a pull "trigger" (a small handle) so the cams move together, then inserting it into a crack or pocket in the rock and pulling on the "stem", a rod attached to the axle. This makes the cams expand and hold onto the rock face, and it is held lightly in position by small springs. At this point the climbing rope can be attached to a sling and carabiner at the end of the stem.
SLCDs were invented by Ray Jardine in 1978 (US patent 4,184,657) and sold under the brand name of "Friends". ("Friend" is now widely used by climbers to refer to SLCDs in general, but properly speaking it refers to the brand now manufactured by Wild Country.) Other popular brands include Camalots, and Aliens.
SLCDs are sold in various sizes to fit a diverse range of cracks from about 1 cm to 15 cm wide.
The invention of SLCDs revolutionised rock climbing because it meant that climbs with parallel cracks could be protected. Furthermore, unlike pitons, SLCDs can be removed easily without causing damage to the rock, and made clean climbing (climbing without damaging the rock) practical on almost all climbs.