This is a special 0.6x C-Mount (MA151/8TR) for Meiji's EMZ-8TR, EMZ-12TR, and EMZ-13TR models only. It replaces the standard Meiji 25mm OD Phototube and provides a low-profile, stable mount for the camera. The 0.6x magnification means it works best for 1/2" or 2/3" sensor cameras.