The light weight billet aluminum standard castle nut is an essential part of an AR-15 carbine receiver extension buffer tube lock ring assembly. This castle nut-lock ring it features standard cuts for proper use with armorer’s wrench and smaller cuts for staking the castle nut. This castle nut will ideally fit onto any standard mil-spec and commercial buffer tubes. The castle nut is machined from a solid piece of billet aircraft grade aluminum type III hard coat anodized with black matte finish. This castle nut it is great for new AR builds or replacing worn part and will not rust.