These flap discs excel on soft metals like aluminum. They don't gum up like a regular zirconia or aluminum flap disc. The stearate coating, which gives the flap disc its silver color, will liquefy under heat and provide a protective coat on the flaps that prevents loading/gumming up on soft metals. These discs can be used like any other discs, but they are specifically meant to for use on softer metals like copper, aluminum and bronze.