This is a focus rack with tail for major brand stereo microscopes. It comes with a 3" (75mm) diameter of annular ring that holds microscope head. It is brand new in factory sealed box. Features & Specifications: Brand new pin-tail focus rack Good for major brand stereo microscopes Focus gear with coarse focus and tension adjustment Diameter of annular ring holding microscope head: 3" (75mm) Diameter of the pin tail: 5/8" (16mm) Focusing distance in vertical direction: 3.