The Williams™ 47476 WAK47-Aperture  Receiver Peep Sight is specifically designed to replace the original open sight with a peep sight. Williams™ WAK47-Aperture Receiver Peep Sights offer shooters unmatched open sight visibility at longer distances than standard fixed open sights. The Williams™ WAK47-Aperture Receiver Peep Sight is compatible with a front fiber optic fire sight. Williams™ Fire Sights gather ambient light and reflect it back to your eye, enabling faster target acquisition. Williams™ Sights do not use artificial light sources to create their sight visibility, making them legal to use in states that do not allow artificial light sources on your firearm while hunting.