Sometimes a compact fluorescent bulb just won't fit into a lamp or fixture (especially the deep pot lights). Its usually because the bulb ballast is a little wider than a typical incandescent. This is where this ceramic extender comes into play. Simply screw in the externder in the existing socket and voila ... you now should have a little more room to fit the CFL. Note: This extends the bulb by about 1 inch (2.5 cm).  For potlights there is an added benefit of bringing the light closer to the edge of the ceiling, hence using more of the available lumens from the bulb.