Leupold Alumina Flip-Open Covers are made from machined aluminum to ensure lightweight durability in any type of weather. These lens covers come in a variety of sizes, from 20mm to 50mm, for use in either objective lenses or eyepieces. These flip-open lens covers are designed with powerful neodymium magnets that hold the cover closed, forming a watertight seal. As an added bonus, the cover flips all the way back into a horizontal position for a low profile