Ergo Castle Nut Features The Ergo Castle Nut is machined from steel to provide a durable long lasting replacement for the factory nut that secures a buffer tube to the receiver extension. It works with commercial military and hybrid spec buffer tubes covering the vast majority of AR-15 and AR variant builds. Properly torquing the castle nut keeps the stock assembly tight and prevents the buffer tube from loosening or rotating under recoil. A black finish matches the factory appearance of most AR lower receivers and buffer tube assemblies. This castle nut is a simple but essential component for any AR build armorer s kit or maintenance toolkit since a worn or damaged original can lead to a loose rattling stock. Steel construction stands up to repeated torquing with an armorer s wrench without rounding or deforming. Keeping a spare on hand is a practical step for builders assembling multiple lowers or performing field repairs. This Ergo Castle Nut for the AR-Platform is available for sale at GrabAGun for AR owners and builders. Ergo Castle Nut Specifications Manufacturer: Ergo Model: Castle Nut Color: Black Material: Steel Compatible Hosts: AR-Platform Weight: 0.06 lbs Available At: GrabAGun