United Shield ARC Rail Kit Black ARC-RAIL-KIT-BK. The ARC Rail System is easy to install and requires no modification to the ARC itself. The ARC Rail adapter installs in the existing ARC rail holes and secures by use of a hex wrench a standard plier and a special hex tool. Some tools and supplies are required but with these basic tools putting together a reliable harness is simplified. The ARC Rail system is designed to fit the X-Force and X-Force X-Frac with new locking mechanisms to ensure that they will not come loose. Wire can be added but only when the proper nomenclature is given. The proper nomenclature must be specified when ordering. The United Shield International ARC Rails are made of glass reinforced nylon and are shaped to fit the Spec Ops and ACH/MICH (Med. and Large.) helmets that have been drilled to the ACH specification. Specifications for United Shield ARC Rail Kit: Manufacturer: United Shield Size: One Size Condition: New Package Contents: United Shield ARC Rail Kit United Shield ARC-RAIL-KIT-BK: ARC Rail Kit Black