What are ''camming devices'' used for

this is a climbing devise that is put in a crack location where weight forces the cam to get wedged even tighter so it will not slip out. On belay!

Cams r used in ''Trad'' or Traditional climbing. They r designed to place in a crack as an anchor or protection(''pro'') from a fall. They r spring loaded & designed to expand as more pressure is applied. The harder the pressure, like falling for example, the harder the cam tries to expand, so it holds it is place in the crack keeping the climber from falling further. Other alternatives to cams r ''fixed'' or passive gear, which do not have any moving parts like nuts & hexes. Cams really became popular in the last 12 yrs. Their ability to expand means the same cam can fit into different sized cracks, really speeding up the amount time it takes to place the gear & allowing the climber to carry less fixed gear which can be cumbersome. Cams r not perfect though & come with their own set of problems. The most infamous problem is ''walking''. With no weight on the cam & rope wagging back & forth, cams will sometimes rock or ''walk'' out of the crack. Another problem is weight, their heavy. If u know the route & sizes of the cracks u may be better off just carrying the correct fixed gear. Finally, they r expensive! Each cam will run somewhere between $60 & $120.
For an avid climber, who is interested in getting into trad climbing, they r diffidently worth the investment.

Otherwise known as Friends (a brand name), ''cams'' r used as chocks which u then clip the rope to.
They're a relatively modern invention in rock climbing, & being used a lot more than they used to be due to lighter & lighter materials becoming available. So instead of using many nuts & especially hexes, climbers (with enough money!) use cams instead.
As other people have mentioned, cams r spring loaded things, u pull a lever & they contract, u place it into a crack or a hole, & then u let go of the lever & it expands again, hopefully filling the gap & sticking fast. They're also engineered so that the harder u pull on them (in one direction anyway), the tighter they grip the rock. They do have a tendency to ''walk'' though, if u do not have a long enough runner (i.e. if only have a short sling attaching it to the rope, as u move up & jiggle the rope about it can ease the cam out of the crack).
They come in many different sizes, from 0.5 (tiny! would not reeeally trust it), to like 9 or something, massive.
They r very expensive, but they're so much easier to place & to remove than nuts & hexes.

Cams r used for techical rock climbing on traditional (non-bolted ''trad'') routes for protection (''pro''). As u climb, u will set pro (cam, nut, hex, sling, etc) in a crack or other feature in the rock & using a webbing runner & a carabiner clip the rope to the protection. You then climb past the protection - if u fall then u will fall to the last piece of protection plus that same distance again before the rope will catch you. When the second climber climbs up to the cam, he will remove it & bring it with him. This is called ''clean'' climbing because u do not damage the rock & do not leave anything behind.

Good Luck