The Leica Rusan MAR Clamp Adapter is the scope-side component of the modular system that enables secure, repeatable mounting of the Leica Calonox Sight or Calonox 2 thermal units to your rifle scope. Precision-machined and available in multiple diameters, it locks onto the objective bell of your riflescope and mates with the corresponding Rusan MCR-M43P (for Calonox 2 Sight and Calonox 2 Sight LRF) or MCR-M52 (for Calonox Sight and Calonox Sight SE) connectors. Note: This listing is for the scope-side clamp only. Must be used in combination with the appropriate Rusan MCR adapter to complete the system. To select the correct size, measure the outer diameter of your riflescope's objective bell and choose the matching MAR clamp (e.g., MAR-30 for a 30 mm housing).