Tronixpro 77mm Pro Series Snap On Lens Cap For Sigma 17-50mm f/2.8 EX DC OS HSM Zoom Lens, Sigma 85mm f/1.4 EX DG HSM Lens, Sigma 120-400mm f/4.5-5.6 DG APO OS HSM Autofocus Lens This lens cap protects lens surface from dust & shock during storage. Unique snap on design allows easy installation onto the lens & one-step removal from the lens. It fits directly onto the lens with a double-action spring design. Microfiber Cloth 77mm Snap On Lens Cap