This Butler Creek flip-up Eyepiece lens cover opens at the touch of your thumb and features a watertight friction mount and semi O-ring that securely anchors the cover, sealing out dust and moisture. The ocular lens covers feature a large push button for quick spring loaded opening when you want to keep your optics protected until the perfect shot presents itself. The ultimate objective lens protection for hunters and shooters, Flip-Open scope covers are custom fit to your scope, create a watertight, airtight seal, and open with a touch of your thumb, so you can put your shot through the narrow window of opportunity in the most extreme conditions. The fast, flip-open design with a silent hinge keeps your eye on the target and won't spook game. It weighs less than an ounce and has been tested to -40 DegreeF..