This M.A.D. site with 4 different apertures provides all apertures on the same plane and can be zeroed to the same point of impact. It has four apertures, rotating the aperture in any direction will bring the next size into view. The small aperture diameter is 0.073" and the large aperture is 0.199". The distance between the top of your rail and the aperture is 35mm. Made by a current US Govt Contractor. Sanitized, no markings.