The Aimpoint® Flip-Up Rear Lens Cover is a solid black cover made with rugged plastic - providing additional protection to the Aimpoint sight lenses. This product fits rear lenses of the CompM4™ series (CompM4/M4s), PRO™, ACO™, and 9000™ series sights. It provides protection against scratches, lent, dust, or sand that may accumulate on the lens. Installation is fast and easy - the pliable material slides over the rear lens of the sight for a perfect, snug fit.