Mounting screws of proper length are typically included with your new lamp fixture. Screws 2 or 21/2 inches long are sufficient for most fixtures. Insert the screws into the attachment screw holes in the electrical box, and tighten each screw four or five turns to hold it in place. Mount the fixture by passing fixture's keyhole slots over the screw heads. Then rotate the fixture enough so the screws are forced into the narrow parts of the keyhole slots.