DoubleStar Car Castle Nut Black. These AR15 Lower Parts brought to you by DoubleStar are constructed from steel for maximum durability. This standard Mil-Spec Doublestar AR346 Car Castle Nut provides a tight secure and reliable fit. Grab the Doublestar AR Car Castle Nut for your tightening needs. Specifications for DoubleStar Car Castle Nut: Manufacturer: DoubleStar Color: Black Fabric/Material: Steel Gun Make: AR Platform Features of Doublestar CAR Castle Nut Standard Mil-Spec Castle Nut Package Contents: Doublestar CAR Castle Nut DoubleStar AR346: Car Castle Nut Black