Fast, flip-open design; custom fit for most scopes * Water-tight, custom-fit friction mounts anchors them to your scope; air-tight semi-O-ring keeps out dust and moisture * Truly ambidextrous; silent spring hinges won"t spook game * Instant action lids pop open at the touch of a thumb * Performs from -40 to 120 Degrees F.; weighs less than an ounce