A Hand is an item used in the Rocking Out quest. When Captain Brass Hand Harry gives a broken hand, it can be "taken-apart" to form a hand. You crack the hand plates from this hand. The rest is useless.
The hand is then combined with 4 other parts (thumb, fingers, brace, and wrist), with a hammer and 2 bronze wires in the inventory, to smith a Brass hand.
The Brass hand is subsequently used to gain the mark from the captain.