Deluxe 2-1/8 inch socket extension non-adjustable medium to medium base. 4KV pulse rated socket for up to 250 watts. Socket Extension easily screws into an existing medium base socket and allows you to extend lamp an additional 2-1/8 inches. The male screw in basefeatures a built-in ratchet mechanism that prevents over tightening of lamp. To use with a metal halide lamp, the fixture must have appropriate ballast.