This steel castle nut locks the receiver extension to an AR-15 lower and captures the end plate so the buffer tube and takedown spring stay put under recoil. The castellated face takes an armorer's wrench for torquing, and the notches give you a surface to stake against so the nut won't back off in use.
Features:
Fits mil-spec receiver-extension threads, not commercial. Torque with an armorer's wrench and stake after installation so it stays locked.
