What is it?

So small - so much trouble! This small item measures about 10mm. It pretty much brought the household to a standstill today. A household appliance had an altercation with the floor and this item popped out. Driven by the, apparently maddening,  philosophy of 'Never, never, never give up' yours truly eventually worked out how to put it back. Can you guess which appliance and what job this item does? I'll give you the answer tomorrow.