The Sigma LCF-86 III Front Lens Cap is designed to protect the lens from external damage and impacts. Built with a hard plastic material, it also protects the front lens element from harmful UV rays of the sun when the camera is not in use. It has a diameter of 86 mm and is compatible with Global Vision lenses. This Lens cap also acts as a barrier against dust and dirt to from entering the lens. It has a system that can be opened and closed very easily. Just push the button on the cap and it opens up. It's as easy as that.