Cam

A cam, short for spring loaded camming device, has several curved lobes mounted on an axle that expand outward when a trigger is released, wedging into a crack and gripping the rock through camming action. Pulling down on the stem increases the outward force on the lobes, which is what lets a properly placed cam hold a fall.

Cams come in a range of sizes to fit anything from finger width seams to wide off width cracks, and most trad racks carry a set spanning several sizes since crack width varies constantly along a pitch. Some designs use a single axle while others use two offset axles to grip a wider range of crack shapes with one size.

Placement quality depends on choosing a spot where the crack is roughly parallel sided and the lobes sit within their working range rather than fully open or fully closed, since a cam placed too open can walk or fail under load. Learning to place and evaluate cams reliably takes hands on mentorship or a course, since a bad placement can look secure and still fail.