Quickly mount the Burris Thermal Clip-On (BTC) to your favorite riflescope using our Smarclip clip-on adapters. Options available are for 30-63.5mm objective lenses. Size is determined by the outside diameter of your optics objective bell. Screw on the adapter to your Burris Thermal Clip-On and secure to your optic's objective lens using a quick-detach cam lever. Burris BTC Adapter 56mm U. S.E. Thermal Smartclip Adaptor 626639