For mounting lenses with 72mm x 1 mounting thread, such as the Rodenstock Rodagon 240mm and 300mm, and Rodagon-G 210mm and 240mm lenses. The flange is secured to the enlarger lensboard with screws, and the lens is then threaded into the flange. This flange has an outside diameter of 95mm. Please verify the mounting thread on your lens. Flange mounting screws are not included.