LBE Unlimited is a quality manufacturer of AR-15 parts and accessories. This particular item is an AR-15 Mil-Spec diameter carbine receiver extension kit. This Complete kit can be used as a replacement unit or as a spare for a new build. This unit comes with all the parts you need to assembly the stock section of the lower receiver. This kit along with it's components are made right here in the USA.
AR-15 Mil-Spec Stock Assembly Kit
Includes- buffer tube" castlenut" endplate" buffer and carbine spring