The HoodMAG 3.0 is designed to fit where the original HoodLoupe 3.0 eyecup was installed. Remove your original HoodLoupe rubber eyecup by pulling the low profile eyecup up and off of your HoodLoupe. Mount new HoodMAG by pushing it over viewing end of HoodLoupe. HoodMAG has a tighter fit than the original eyecup and will stay in place once mounted.
The slip ring mounted within your HoodMAG eyecup will allow diopter adjustment without rotating the eyecup. Diopter adjustment remains the same, just twist the HoodLoupe viewing end in or out to set for your vision.