Please note, that you are able to open the cuffs by yourself with enough force even without the key, because of the stiffness of PLA.

The key is a normal handcuff key and not included in this design.

For a finished thumbcuffs, you need:
-1x "main" body
-1x “upper” body
-2x “side”
-2x "safe"

and 2 springs with a diameter of 5,5mm (photo)