This was pulled off of the Cambridge Instrumental/B&L Zoom 500 Trinocular Microscope with Light Table. This is the 4x Bausch & Lomb objective that fits this microscope. Beautiful wide angle achromatic coated optics. Front lens clear diameter is 13mm and the rear lens clear diameter is 15.5mm. The front and rear lenses have a bluish/purple anti-reflective coating. The front lens has a fine tuning focusing mechanism. The rear lens housing which goes into the microscope body is 32.5mm in diameter with two pins sticking out the sides for clasping in place. The base is 74mm long by 56mm wide. The whole assembly is 75mm long by 77mm wide.