This Remington manufactured early variation rear receiver insert has the two "threaded" holes on the underside designed to attach the early variation two hole magazine lock using two machined screws. This rear receiver insert is for the early model 521-T Junior Special  bolt action rimfire rifle and is in very good condition with light wear. (file photo)

Note: Firearms with the following date codes have been observed with this part: OSS (July 1947)