Gehmann Mirror Disc Attachment For Rearsight 509 Rearsight mirror disc attachment Brings a new concept to rearsight disc attachments with a reflective mirror towards the shooter's eye bearing a contrasting black insert disc Concentrates the focal point of the target in the shooter's mind Fits all standard 1" rearsight discs or irises This tool attaches to the shooter's rear sight iris and allows the shooter to double check that their head placement and sight alignment is correct. If you have proper sight alignment, you should not be able to see any part of your eye. If your sight alignment is not perfect, you will be able to see that part of your eye looking back at you.