Hammer is a freakish-looking hulk with a left arm that appears twice as thick as his right.
A Dance with Dragons
According to Kem, Hammer is drunk more often than not. He tells Tyrion that Brown Ben lets it go, but that one day they'd get a real armorer. He is sleeping off a drunk when Tyrion and Penny arrive at the forge to pick out some company steel after signing with the company, just as Kem had predicted. Nail is there to admit them to the wagons to choose weapons and armor. Jorah Mormont was already choosing his armor from the wagons when they arrived.