This Remington manufactured first variation breech block is for the early model 12 slide action rimfire rifle in 22 S, L & LR caliber which uses the flat type firing pin. The overall condition is very good with light wear and some specks of rust.  (file photo)

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

12-A: 3867, 100823 & 374065

12-C: 229853, 408616, 409187, 500140, 597770, 600364 & 607712