Ring to attach to a rehusable plastic cup so the cup can hang from a carabiner attached via keychain.

It does fit these typical plastic cups from catalonia:
https://shop.ecofestes.com/ca/shop/productos/ver/128/

Don't know if it will fit cups elswhere

If it doesn't you can just edit it on thingiverse:
https://www.tinkercad.com/things/4vNDsQINF3j