These two GG&G optical mounting rails were designed to mount easily over the integral rails of the AR-15/M16 flat top receiver and work in conjunction with any of GG&G's back up iron sights. The rails mounting brackets raise the line of sight by 1/2 inch"" to offer a proper cheek weld when optical devices are attached. In addition"" they serve to protect the flat top receiver's integral rails from the damaging wear associated with lever type quick-release mounts"" especially those without buffer pads. The Standard Rail is employed mainly as a riser for conventional optical sights. When mounted with a GG&G back up iron sight"" it is flush with the end of the receiver.