Wikipedia
Camalot, or cam, is a brand of spring-loaded camming devices, manufactured by Black Diamond Equipment, Ltd.
The device is used in cracks to secure ropes while rock climbing.
There are two types of Camalots, those with four lobes (original Camalots and modern C4 models) and those with three lobes (Camalot C3s). The original Camalots and the C4s utilize a patented dual-axle cam system, resulting in a slightly higher expansion range than for a similarly sized single axle unit, and also resulting in increased strength, allowing placement as a passive stopper. C4s range from the small #0.3, to the rarely seen massive #6.
Black Diamond has also announced the Camalot X4, which have a flexible cable stem similar to Aliens or Metolius Master cams. The X4 were released in Spring 2013.
C3s are single axle units designed for smaller, narrower placements, and range from a tiny #000 to #2. There is some overlap between the C4 #0.3 and the C3 1 and 2. As with most microcams, the C3 #000 is rated for aid climbing only.
Camalot lobes were designed to have a logarithmic spiral shape, resulting in a constant angle between the cam and the rock at each contact point; this constant angle is designed to always provide the necessary friction to hold a cam in equilibrium.