Story time. A paper mill decided everything had to be "5s'ed" as we called it. That meant that anything that didn't have a purpose got shitcanned because you couldn't keep it. Coffee cans full of random nuts and bolts, old parts no one could ID... all gone.

So the mill decided to test a new type of refiner plate. These are megawatt grinders with 4' diameter heads. The new plates were smaller and needed a donut ring around the outside of the housing to fill the space. The mill liked the plates, so when the new design plates were worn, they pulled the last set of old plates from stores and ordered new type plates. They set that filler ring aside for future use. Some one discarded it in a 5S audit. When the last set of old plates wore out, they have only the new design in stores but no one could find the filler ring.

Don't you love those efficiency experts?