Sniper AR-15/M16 Receiver Extension Castle Nut Mil Spec Black. 56/.308 Receiver Extension Castle Nut for Mil-Spec Commercial and Pistol Buffer Tubes. Precision machined from Chrome Steel. Specifications for Sniper AR-15/M16 Receiver Extension Mil Spec Castle Nuts: Manufacturer: Sniper Gun Model: M16 AR-15 Condition: New Color: Black Fabric/Material: Chrome Steel Quantity: 1 Features of Sniper AR-15/M16 Receiver Extension Castle Nut Mil Spec: Steel castle nut Package Contents: Sniper AR-15/M16 Receiver Extension Castle Nut Mil Spec What firearm models does the manufacturer say Sniper AR-15/M16 Receiver Extension Mil Spec Castle Nuts is compatible with? The manufacturer suggests that Sniper AR-15/M16 Receiver Extension Mil Spec Castle Nuts is compatible with AR-15 M16Sniper ABNT02: Sniper AR-15/M16 Receiver Extension Castle Nut Mil Spec Black