Leica's Rusan Sight Adapters allows you to join a Leica Calonox thermal Sight with a rifle scope. It's a throw-lever tensioning sleeve that threads onto the eyepiece end of the Calonox and slides over the objective lens housing.The Rusan Adapter is a simple way of attaching a thermal clip-on device to your day scope's objective. Simply slip it over the front lens of your scope and move the lever to the " clamp closed" position.The adapter slips over approximately 1.4" of your objective lens so there is lots of clamping surface area for a great hold. The inside of the adapter is lined with a special film to provide for extra gripping power and assures a scratch free attachment. Note: To determine the exact model you need consult the list below or measure in millimeters the outside diameter of your scope's objective lens at its end. The measurement needs to be exact so use calipers.