The Ultradyne C4 Rear Aperture Insert utilized Dynalign Technology allowing for a concentric sight picture. Dynalign's circle-within-circle sight picture allows for faster sight picture acquisition. The use of the front aperture further reduces parallax affect which makes accuracy less depend on precise sight alignment. Dynalign is a faster and more accurate sight picture that can improve your shooting performance. Designed specifically for Ultradyne C4 Rear Sights.