The Kaiser Plastic Lens Cap is like an old style push-on style cap. It is designed to fit any camera or enlarger lens, binocular, tele-, micro-, or spotting scope lens. To use one, measure the outside diameter of your lens barrel. Order the cap size that is 1 or 2 millimeters larger than the size measured. The cap should fit snuggly but not so tight that it is hard to remove.