This is a set of two dark chrome skull-design knobs for knurled-shaft 6mm potentiometers. These knobs make a great, inexpensive finishing touch for your special build, and provide a nice "premium" look that plastic knobs just can"t give. These knobs are metal with a plastic insert that fits over the pot shaft, and also include a set screw that can be used to tighten on the pot. shaft. A small allen wrench is included with each pack for use with the set screw.