For a 16 year old boy, who had an accident and lost part of his thumb, I designed this thumb. I have used the thumb of Gyrobot's flexy-hand and designed a new thumb phalanx. The linkage and bracelet design I remixed from the Knick's prosthetic finger. The thumb can't bend much, but for this boy it really works well enough to grab things like a coffee mug or the controller of his game computer.

Please be aware that I have just made one thumb and it hasn't been tested much, but since there a not yet much thumb versions on thingiverse it uploaded it anyway. You never know if my remix of the flexy-thumb can help someone else.