Round piece of steel with a hole in it.
WARNING: ONLY FUNNY TO ENGINEERS.
Engineers are sometimes idiots.
Like when they need a washer. 1/8" thick, 1/2" id and 1 1/4" od. And they make a drawing of the washer. And then call 3 machine shops for quotes. And then select a machine shop to make the washer. And in the end the machine shop charges $150 for the washer. At McMaster Carr the exact same washer is $7.89 per Pack of 25. If we wanted 25 it would have cost us $3750.