C clamps are a common way to attach heavy stage lights to a lighting truss. A C clamp is shaped like a "C." The opening of the clamp tightens around the truss bar securely, then the light is attached to the clamp with a screw and bolt or other specific attaching mechanism. Over time, C clamps can scratch or dent the truss, but the wear and tear is normal. Lights typically hang down underneath the truss with a C clamp, but can sit on top of the truss as well. Use ladders and spotters for safety when hanging lights on a truss with a C clamp.
An O clamp is another way to attach a light to a truss on stage. An O clamp is shaped like an "O" and tightens all the way around a bar on the truss, providing a 360 degree secure attachment, whereas a C clamp leaves an opening. O clamps are less likely to scratch or dent the truss. The light attaches to the O clamp with a screw and bolt, similar to a C clamp. Lights typically hang down from the O clamp when attached to the truss.
An S cable is another option for attaching heavy stage lights to a truss. S cables are made of braided metal, and wrap around the truss bar completely. They are flexible, so the design of the S cable naturally tightens as much as possible around the bar, like wrapping a string around your finger and pulling to make it tighter. On the bottom of the S cable are clips to hold the lights. Because of their flexibility, S cables allow the lights to slightly swing or move when fastened to a truss, so if your lights need to be completely stable, opt for another clamp.