I modified this from ChaosCoreTech's awesome Wall-e model. I felt like the hand needed to have a thumb. I designed the thumb to plug into a modified version of the hand file that has a pocket cut into it for the thumb to plug into. I also made a relieved area in the hand that reflects the hand design of the actual Wall-E character just for fun.

I printed the thumbs standing up with adhesion. Of course you may have luck doing it a different way but this worked for me. I printed the thumb with support because of the radial design of the wrist area.