If you are using the Gen 1 Universal Optic Adapter & you want to use the new Smart Bracket or Mag Plate you will need one of these. The new GEN 2 Universal Optic Adapters have a dual thread option where the GEN 1 Adapters had just 1. The Smart Bracket and the Mag Plate use the smaller thread. This matching ring will allow the older GEN 1 Universal Optic Adapter to work on the new products.