In stagecraft, a c-clamp can refer to a number of different pieces of hardware, depending on its intended use.
In stage lighting and sound a c-clamp, also referred to as a pipe clamp, is used to attach a larger piece of hardware, such as a lighting instrument, a speaker, or a dimmer, to a pipe or batten. Newer c-clamps tend to be constructed of aluminum, although steel is also available.
C-clamps function by affixing a bolt (the "shaft bolt") to the hardware they are to hold in place, such as through the yoke of a lighting instrument, and securely fastening this bolt to the clamp shaft. The open end of the clamp is then placed over the batten, and a bolt (the "clamp bolt") is tightened to secure the c-clamp. C-clamps for stage lighting fixtures usually also have a pan screw (also known as a "grub bolt"), which when loosened will allow the clamp shaft, and therefore the fixture, to be rotated 360 degrees while maintaining a secure connection to the batten.
When using c-clamps care must be taken to not over-torque the clamp bolt which affixes the clamp to the batten. If this bolt is overtightened, it can easily dimple or "drill" into the batten seriously compromising the strength of the batten.