A fitter is simply the way the shade connects to your lamp. Most lamps have spider fitters. Other common fitters include UNO or clip-on fitters. Check your existing lamp against the diagram and descriptions below to determine what type of fitter you need.
Harp/Spider Fitters: If your lamp has a harp you will need a shade with a spider fitter. The spider fitter is part of the lampshade itself. It sits on top of the harp and is secured by a finial.If your new shade is not EXACTLY the same size as your old shade, a new harp may be all you need for a perfect fit. Harps typically vary from 7” to 12” and they affect the vertical position of your lampshade. If you do not have a harp but wish to use a shade with a spider fitter you must also purchase a harp. Harps are made in different sizes, which affects the vertical position of the lampshade. The most common finial thread size for harps is 1/4"-27.
UNO Fitters: If your lamp requires an UNO fitter you must purchase a lamp shade that has an UNO fitter. The UNO fitter is built-in to the lampshade. There are two types of UNO fitters, slip-UNO and threaded-UNO.
a) Slip-UNO fitters: sit on the socket and are held in place by the bulb.
b) Threaded-UNO fitters: typically for down-bridge lamps and feature a screw thread for installation above the downward-facing bulb.
Clip-on Fitters: Clip-on lamp shades are typically for chandeliers and wall sconces. The clip fitter is built into the lamp shade and clips over a standard medium or candelabra bulb.
Reflector Bowl Spider Fitters: If your lamp has a reflector bowl inside the shade, a reflector spider fitter may be needed to secure its position. These fitters feature grooves in the spider arms for the secure positioning of reflector bowl. Reflector bowls are not sold as part of the lamp shade - they are usually shipped with the lamp base.