Rusan Adapters are a simple and effective way of attaching a thermal clip-on device to your scopes objective bell. Once the adapter is screwed on to your thermal clip-on you simply slip it over the front lens of your scope and move the lever to the clamp closed position. The attachment takes just a few seconds. The Rusan adapter slips over approximately 1.4" of your objective lens so there's 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.