Original Item: The barrel nut (berwurfmutter) of the famous German MP38 and MP40 machine pistols was locked in place by a thin steel lock washer that was peened into place after the barrel nut was tightened to the correct torque setting. These rings were usually ruined when the guns were disassembled, and therefore are very rare. The German nomenclature for the lock washer is Sicherungsring, or security ring.
