Brass-plated 3 terminal 2 circuit turn knob socket that works in conjunction with a secondary socket (like a hurricane or "Gone-with-the-Wind" lamp). It turns on bottom light, top light (bottom light goes out), both come on simultaneously, then off. Complete 3-piece socket that has bottom cap with 3/8" threaded hole (works with 1/8 IPS pipe). No set screw. (Not technically a nite-lite socket itself, but we described it so because it prevents customers from buying that need the more traditional off-on or 3-way socket. They look the same, but this has 3 terminals and the others have 2 terminals.)