The Fast Cap™ with Metal Ring is truly a winner. It is not only loss-proof, but it's dust-proof as well thanks to the integral semi-"O" ring seal. The wrap-around design of the Fast Cap™ with Metal Ring lid effectively protects the rim of your lens or filter as well as the valuable optics. The threads in the metal ring attach easily and securely to both new and older lenses or filters. Once the metal ring is attached to a lens or filter, the base stays in place when the hinged, spring-loaded lid is flipped open by a flick of the thumb. The cover can be adjusted for the most convenient position of the opening tab. The Fast Cap™ with Metal Ring is available in a universal design to fit most normal/telephoto and wide angle lenses.