This nutcracker is designed to highlight the strength characteristics of Innofil3D filament for their recent contest. The nutcracker is printed in their recycled PET and is subjected to a lot of flex, tension and pressure at the same time. And still, it can crack walnuts with ease! It is designed to fit the average walnut, but other same-sized nuts should work as well.
Please note: you will need the right filament with the right amount of flex as well as strength. I have tested mine for days and it is still going strong, but I don't have any long term use experience (yet). It may break after flexing it excessively and fatiguing the plastic. This should be seen more as a proof of concept to impress your friends than an everyday household item ;)