Alumina Flip Back Lens Cover 50mm Post 2004 Scopes by LEUPOLD MOUNTS & ACCESSORIESAlumina® flip-back lens covers – feature powerful neodymium magnets to hold them securely closed and triple O-ring seals for maximum protection from the elements. Their machined-aluminum precision construction and quick and easy operation and and a low-profile position when open make Leupold's flip-back lens covers stand above the rest.