Fortis Manufacturing Standard Castle Nut Black. If you're trying to save ounces this is a great way but without sacrificing durability. The castle nut will fit onto mil-spec buffer tubes and quickly upgrade the form and function of ybuild. You will need a standard stock wrench to install Specifications for Fortis Manufacturing Standard Castle Nut: Manufacturer: Fortis Manufacturing Gun Model: AR-15 Condition: New Color: Black Fabric/Material: Aircraft Grade 7075-T6 Aluminum Quantity: 1 Features of Fortis Manufacturing Standard Castle Nut Material: Aircraft Grade 7075-T6 Aluminum Weight: 0.2 oz You will need a standard stock wrench to install Type III Hardcoat Anodize made in specialized factories Package Contents: Fortis Manufacturing Standard Castle Nut What firearm models does the manufacturer say Fortis Manufacturing Standard Castle Nut is compatible with? The manufacturer says that Fortis Manufacturing Standard Castle Nut is compatible with AR-15Fortis Manufacturing CN-Stand: Standard Castle Nut Black