This is a heavy-duty pin-tail focus rack for major brand stereo microscopes. It comes with a 3inch (76mm) diameter of annular ring that holds microscope head. Brand new heavy-duty 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: 3inch (76mm) Diameter of the pin tail: 5/8inch (16mm) Focusing distance in vertical direction: 1-3/8inch (35mm) Type: Accessories