Basics of Cams
Cams are meant to protect small to large cracks. Cams provide (to a limited extent) multi-directional protection.
Cams work by contracting two set of lobes then placing the cams into a crack smaller than the expanded lobes. By releasing the trigger, the springs push the cam lobes against the sides of a crack. Cams allow you to make placements in parallel cracks (parallel cracks are difficult to protect with passive protection). The force of the lobes on the rock increases proportionally with the weight being pulled down on the cam (making a solid placement).
Cams are also known as SLCD's, "spring loaded camming devices".Full Article