Replaces existing SKS receiver cover; Provides Three Rails for mounting and Optic on top and accessories on the sides like a Flashlight and/or Laser; The two side rails can be mounted in several positions for mounting flexability, they are also removable; Four side set screws allows you to lock the receiver cover to the SKS receiver for a secure fit; Receiver Cover is manufactured slightly longer by a few thousandths, so that it can be hand fited to the various manufacturers of the SKS rifles; See-Through design, which allows you to still be able to use the Iron Sights when mounted onto the SKS rifle; Aluminum (Rail) and Steel Construction (Receiver Cover); NcSTAR Patented design: Patent # D543,605; Black Finish; NcSTAR One Year Warranty