Leviton Turn Knob Socket Lampholder. Leviton offers a complete selection of incandescent, fluorescent and specialty lampholders. Incandescent and fluorescent styles are available in a wide range of ratings and materials to suit any residential and commercial need. Medium Base complete, aluminum shell incandescent lampholder. Removable turn knob, single circuit. 1/8 IPS tapped bushing with set screw.