This new Aperture Set for the TechSights 200 peep sight allows you to change peep-hole sizes to suit the available light where you're shooting. It works much like a camera aperture in that, the smaller the hole, the better the focus. Of course in low light, you need a bigger hole to be able to see. And in bright light, you can use the smallest aperture and see the clearest sight picture. This set allows you to use the best size peep-hole (aperture) for the available light. The set is designed only for the TechSight 200 model (and won't fit the TS100). If you have or are ordering a TechSights 200 sight, this is a great add-on! For TechSights and more... Please see our M1 Carbine 10/22 Tribute Page.