Precision Reflex Armalite Receivers .308 SPR Full Top Tactical Rail System 19in Black. This rail has a full 1913 rail across the top. Rails come with mounting screws for attachment to forearm rail. The rail is 19in in length. Add .475in to the elevation of the receiver. There are 3 cross bolts that tie the top rail to the receiver and 4 #10-32 socket head screws and a bar nut that secures top rail to forearm. Top rail is designed to work with PRI round 308 forearms. This forearm is designed to work with AR10 receivers or receivers that are 1.328in off bore center to top of receiver. Specifications for Precision Reflex .308 SPR Armalite Full Top Tactical Rail System: Manufacturer: Precision Reflex Color: Black Finish: Hard Coat Anodized Fabric/Material: T6 6061 Aluminum Gun Rail: Full Top Rail Gun Model: AR-10 Width: 1.325 in Height: 0.475 in Weight: 12.7 oz Quantity: 1 Features of Precision Reflex .308 SPR Armalite Full Top Rail System: Rail is constructed of T6 6061 hard coated black anodized aluminum This rail has a full 1913 rail across the top Rails come with mounting screws for attachment to forearm rail The rail is 19" in length Add .455" to the elevation of the receiver There are 3 cross bolts that tie the top rail to the receiver and 4 #10-32 socket head screws and a bar nut that secures top rail to forearm Top rail is designed to work with PRI round 308 forearms This forearm is designed to work with AR10 receivers or receivers that are 1.328" off bore center to top of receiver. Package Contents: Precision Reflex .308 SPR Armalite Full Top Tactical Rail System Precision Reflex 03-072-SPR-A: Armalite Receivers .308 SPR Full Top Tactical Rail System 19in Black