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 C-clamp's operation involves fastening a bolt (referred to as the "shaft bolt") to the hardware it needs to secure, like the yoke of a lighting fixture, and then tightly connecting this bolt to the clamp shaft.