Approximating the quintessential and ubiquitous LEGO toy "hand", I designed one from scratch, got it manufactured in stainless steel and spray painted it with yellow acrylic color. Here is a life size LEGO "hand" used in advertising and action:
Here is a prosthetic approximation that I designed myself, that is Ready To Wear, and so in its own way, my newly designed item is the first real humanly wearable and thus real Lean Ergonomic Grip Orthogonizer (L. E. G. O.) "hand". With that it may challenge your views on anthropomorphism, functionality, and on the Uncanny Valley, and it does challenge the LEGO makers that believed theirs was only an actual toy "hand".
As it looks when the L. E. G. O. "hand" is mounted on my prosthetic arm.
Using a drill with this L. E. G. O. hand is easy - as you can see, all that is needed to submit the button into function is a single paper towel.
Holding an espresso cup is really not a problem. The reason is that I do not rely on plastic deformation for the "hold" mechanism - much rather, this design has a small edge (at the bottom).
It was really designed to perfectly fit a beer can, however. For that it has also the small edge at the bottom. So really this is not a LEGO hand - it is designed after that, but it is mechanically different in the way it works, and for that it has clear design differences.
Here is the hand being used to drink a beer.
Using a water tap is easy with this sophisticated while simple tool.
Another shot of the L. E. G. O. "hand" as it is.
And now, opening and closing a cupboard, as hailed as important for wearing a prosthetic arm.
You can get your own stainless steel L. E. G. O. hand (download STL below): as it is, stainless steel can be 3D printed but it is not quite as cheap as PLA - but then, it does not break nearly as fast. I cannot advise to use Shapeways as their metal prints are really crap, quality wise, but if you try the services of materialise, you may get better instances.