Prosthetic hand design, parts are very small, I recommend printing them at at least 180% maybe 250% for an adult. The finger joints can be printed on their sides, just make sure they are printed with the connecting male/female parts facing up in order to avoid needing any support structure.

Finger 1 (*5) - first finger joint

Finger 2 (*4) - second finger joint

Finger 3 (*4) - third finger joint

Finger 1 + Thumb tip (*1) - Thumb

Thread an elastic string (~8") Through the top of in each finger and down through the palm, tie it off tightly at both ends. (I recommend using one string for the first and second fingers and another string for the third and fourth fingers, thread it up through one and then down through the next)

Thread a strong and thin non-elastic string (~18") through the bottom set of holes. Tie it off at the finger tip (I usually tie it around the base of the elastic knot at the finger tip, Tie the other end off at the end of the gauntlet)

When you pull the plain strings coming out of the base of the palm, the hand should close.

*number needed for full hand

THIS HAND IS TOTALLY UNTESTED... but feel free to test it! :)

Also I have not yet made a piece to connect the gauntlet to the palm