A broken cannon barrel (broken) is used when repairing dwarf multicannons within the Artisans Workshop. It can be picked up from the cannon barrel desk in the repair room after the base and stand have been repaired. It can be repaired on an anvil into a partially broken cannon barrel. Upon completely fixing it completely, it will become a cannon barrel.
This item cannot be taken outside of the repair area. It can be re-obtained from Isak if you have left the area after obtaining it.