extra washer after cleaning/restoration

i just bought a super old KitchenAid model 3-C. I did a deep clean on it, taking most of the motor apart and cleaning out the gearbox. I've put it back together and it seems to work fine, but I've got an extra washer (as seen in photo) Usually I would pretend I didn't see the it but I'm trying to better myself lol. Does anyone know recognise it, or know where in might go?