The Trinity Force Mil-Spec AR Receiver Extension Kit features a Made in USA Buffer Tube constructed from aircraft-grade aluminum with rolled threading, it is hard coat anodized for maximum corrosion and wear resistance. The Action Spring is also Made in the USA and is constructed from music wire and zinc plate coating. This kit comes complete with 3oz carbine buffer as well as steel melonited castle nut and lower receiver end plate. This assembly kit will fit on all Mil-Spec AR 15 lower receivers. It is also compatible with most AR 308/AR 10 rifles but requires a modified buffer and spring for proper operation. For your safety, Trinity Force recommends this part be installed by a competent, qualified gunsmith/installer with an understanding of the weapon platform that the part is being installed on. Always make sure the firearm is unloaded and pointed in a safe direction when working.