This is a focus rack for major brand stereo microscopes Olympus Nikon Zeiss Leica etc. It comes with ball bearing and 3inch (76mm) diameter of annular ring that holds microscope head. Brand new focus rack with ball bearing Good for major brand stereo microscopes Olympus Nikon Zeiss LeicaFocus gear with coarse focus and tension adjustment Diameter of annular ring holding microscope head: 3inch (76mm) Diameter of opening for stand post (arbor): 1-1/4inch (32mm) Distance between central ne of annular hole and that of microscope body: 5-1/2inch (140mm) Focusing distance in vertical direction: 2inch (50mm) Type: Accessories