An insulator that is essentially thin and flat, with one through hole centrally located. The general shape may vary by the addition of features such as beveled edges, indented surfaces, through hole keys, and/or peripheral flats. The thickness measured between the two parallel bearing surfaces must not exceed 25 percent of the outside diameter or the shortest distance between peripheral flats. The thickness measured between the two parallel bearing surfaces must not exceed 25 percent of the outside diameter or the shortest distance between peripheral flats. Excludes items with more than one hole. See also insulator, disk; insulator, bead; insulator, bushing; and insulator, plate