1. Carpentry. Holding device shaped like the third letter of the alphabet used to temporarily affix two surfaces together, often while an adhesive cures. Sized in inches (or mm) referring to the maximum jaw opening. http://www.cksinfo.com/construction/tools/clamps/index.html 2. Lighting. The primary method of attaching a conventional lighting fixture to a horizontal 1.5" I.D. BIP. See also the thread: http://www.controlbooth.com/forums/lighting/10437-c-clampery.html.