smith's assistant; striker
Traditional term for the assistant who strikes the metal with a large hammer in response to the master smith's lead. Used in the context of Japanese swordsmithing or metalworking.
In swordsmithing, the striker swings a large hammer in time with the master's signals.
large hammer (used by a striker)
The heavy hammer wielded by the assistant smith. Often used in the phrase 向こう鎚を振るう.
The large hammer is too heavy to swing alone.