Mushroom Head Pushbuttons. The Harmony 9001K range of mushroom head pushbuttons are available in various different colours and with different types of pushbutton actuation. The 9001 K series of pushbutoons are heavy duty products designed for heavy duty applications. Rugged and chrome-plated for most installations Maintained, push-pull or spring return versions Integrated earth ground connection (no ground wires required) Easy installation with octagonal ring nut Rated to IP66