Spider Fitter Shades
Lamp shades with a spider fitter, feature 3 or more 'arms' which reach across the top of the lamp shade frame, in towards the center. They join at a ring which has a hole in the center.
The ring with the hole rests on top of a 'harp fitter', which is attached to the base of the lamp. The harp fitter is a wire structure which rises up from below the light bulb socket (the saddle), up around the bulb and joins at the top, supporting a screw thread.
The screw thread pushes through the spider-fitter's central ring and protrudes through the other side. A lamp shade finial is then screwed on top to secure the lampshade to the lamp.
Sometimes the arms of the spider fitter, which are part of the lamp shade's metal framework, may feature notches, who are designed to rest on top of a glass reflector bowl which may be part of the design of the lamp.