These are a pair of brand new 5X microscope eyepieces. They are Achromatic (International DIN/JIS) standard size with outside diameter of approx. 30mm and an aperture of 11mm. They fit most common size stereo microscopes. Give your microscope a boost with greater power & clarity at a fraction of cost. Features: 5X Magnification Power 30 mm Mounting Size (in diameter) Wide Field of View