Scenic/Costumes. A tool used to perforate a pattern so as to allow pigment from a pounce bag to transfer the pattern.
Pounce Wheel from Rose Brand
May also be called a Wartenberg wheel (Wikipedia link).
Lighting. Some say the life of saturated colors can be extended by first running this tool across the gel. Others argue this just provides a mechanical failure for the heat to start to melt the gel. http://www.controlbooth.com/forums/lighting/11753-stop-blowing-holes-my-gels.html