A sturdy hook to hang bird feeders from tree branches. So far, have been squirrel-proof! (as in, the little chaps haven't eaten through it).

Has a small gap to get the feeder off and on, at an angle to discourage animals (I'm looking at you, squirrels) from unhooking and stealing the entire feeder - which they have done before on other hooks.

Branch gap also fairly small for the same reason, but you could put it on further up the branch and then move it closer to the trunk.

Printed in ABS or ASA for durability outside. Made the first prototype in PLA and it lasted about a fortnight. PETG might also do it.