The lampshade fitter is the metal framework that attaches the shade to the lamp. There are three basic types of fitters:Clip-on fitters have a clamp that clips directly onto the bulb.Spider fitters have three prongs that meet in the center of the shade. These fitters attach to a lamp harp, which is a U-shaped wire structure that surrounds the bulb. Some shades include a harp, but many require you to purchase the harp separately if the lamp doesn’t already have one in place.UNO fitters have three prongs that attach to a metal ring that sits on the socket that holds the bulb.