This Remington manufactured third variation breech block is for the later model 12 slide action rimfire rifle in 22 S, L & LR caliber which uses the round type firing pin. This third variation breech block has the narrow locking block on the upper front section and is in very good condition with light wear and some specks of rust staining. (file photo)

Note: Remington model 12 slide action rimfire rifles with the following serial numbers have been observed with this part: 

12-A: 741138 &  802984

12-C: 663586