XM4SD Carbine Aluminum Quad Rail is designed to exceed the requirements of the US Army for improving zero retention and repeatability. With a slimmer profile, this Picatinny quad rail improves durability, reliability and maintainability while interfacing with all issued weapon system components. The XM4SD has four full length rails and the top rail, with the existing flat top rail, creates one long monolithic rail. It has four push button sling mounting points at the front and back, and slots around the rails to provide maximum ventilation. CNC-machined from aviation grade aluminum to MIL-1913 standards, the XM4SD has a hard anodized black oxide finish for durability and ease of maintenance.XM4SD Carbine Aluminum Quad Rail requires delta ring removal.