In letterpress printing, a quoin is a mechanical or wooden wedge placed between the type matter and the metal frame. By turning a key or driving the wedge with a mallet, the printer expands the quoin to apply lateral pressure, locking the entire form tightly together so it can be moved to the press without spilling.
Heard on the job
Grab the quoin key and tighten up that form before we lift it off the stone.