Centurion Arms C4 "diopter” style iron sights are for use with AR-15 or M4 flat top receivers. The sights are designed to the correct ergonomic height for the standard AR-15/M4 flat top receivers in any of the popular calibers including (5.56, 300BLK, 9mm ect) for the proper feel and rapid sight acquisition. The rear drum has four different apertures, allowing the shooter to rapidly adjust for different light conditions. It uses a standard HK type adjustment tool for windage and elevation. The front sight mounts to any commonly available same plane rail style hand guard that is the industry standard. It uses a standard fixed blade which can be replaced with the tritium front sight blade commonly sold for the HK91/94/93/ and MP5’s. Both front and rear sights are also compatible with any standard AR-15/M4 sights, including any standard height back up iron sights or the detachable carry handle rear sights. This offers the shooter maximum sight options. The Centurion Arms sights also take up a minimal amount of rail space leaving plenty of room to be used as back up iron sights in conjunction with Aimpoint, EO Tech and most other readily available red dot sights.