The long metal tool a follower has to use to free their leader’s nuts when they
get stuck in a crack. It should be thin (to account for even
the smallest nuts), and ideally have a leash so you don’t drop it. It should also have a hook on the working end. On the handle end a flat spot is nice so when you have to hit it hard to remove their nuts, you don’t hurt your hand.
A person with a rack should
absolutely own a nut tool.
Also called a pro key. An important part of your traditional rock climbing toolkit.