Broken cannon cogs are used when repairing dwarf multicannons within the Artisans' Workshop. You will receive 10 broken cogs after removing them from a broken cannon base. You should try to repair the broken cogs on an anvil with a hammer, to make fixed cogs. The repaired cogs should then be added back onto the empty cannon base to give the repaired cannon base.
There is a chance that a damaged cog will be destroyed in attempting to repair it. In this case you must make a Cannon cog from scratch using a Steel ingot II and a Cog mould on a furnace.
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.