Butler Creek Flip-Open Eyepiece Scope Cover Fast, flip-open design custom fit for most scopes instant action lids pop open at the touch of a thumb Water-tight, custom-fit friction mounts anchors them to your scope air-tight semi-O-ring keeps out dust and moisture Dimension given are the inner diameter so measure the outside diameter of your scope tube to get the proper fit performs from -40 to 120 Degrees F,weighs less than an ounce In order to get the right fit you need to a use a caliper to find the exact size of the objective and eyepiece bells and then check the size chart for caps Sizes listed in table subject to change. For best accuracy, please check fit of caps before purchase