This AR steel castle nut is an essential piece of an AR 15/AR-10 carbine buffer tube stock assembly. The steel AR-15 castle nut secures end lock plates on an adjustable stock. This steel castle nut fits Mil-spec Military, Commercial and Hybrid buffer tubes on the AR-15, AR10 LR-308 carbine and pistol. This steel castle nut is perfect for the AR series rifles for upgrading existing components or replacing worn or broken parts. This castle nut has a limited lifetime warranty and is made in the USA from solid steel with a matte black finish.