The newly designed 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. Once attached to a lens or filter with metal threads, 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.