This is intended as replacement fingers for a person with a wrist and palm, but no digits, most commonly the congenital amputation Amniotic Banding Syndrome (ABS). It lacks the elastics common to this type of assistive device. There are two main reasons for a mechanical extension system:

1. With elastic systems, the user fights resistance. Furthermore, the smaller an object the device grasps, the greater the resistance from the elastics. Mechanical extensors lend the user much greater strength, especially when grasping small objects (ie. those which require greater flexion)
2. Elastic systems only engage the flexors of the wrist, which can lead to unbalanced anatomy and repetitive strain. The Flextensor relies on both the user's wrist flexor and extensor muscles, which should be preferable from a therapeutic standpoint.

The only part here that needs to be printed with any support is the rod. 'TFRod' is a separate file, and should be printed separately, with support.
With a large print bed, or at a small scale, you can print just TalonFlexLeft or TalonFlex Right, plus TFRod. 
If you have a smaller print bed, or need to print large-scale, 
print:
TalonFlexLeftA, TalonFlexLeftB and TFRod for a left hand
TalonFlexRightA, TalonFlexRightB and TFRod for a right hand
All the parts are also available here individually.
I built this with my son in mind, a 20-year old with a large right hand and no fingers on his left hand. Tolerances have been calculated for a scale of 160%, about a men's large or extra large. If you print it smaller, joints will be tighter, and you will spend more time sanding it down. Also I print in ABS, so I need to count on some shrinkage. Abs shrinks as it cools, and then even more when I smooth it in acetone vapor. 
So if you're printing in PLA and/or at scales below 160%, you are now forewarned. When I adjust this model for kids and PLA, I'll tweak the gaps. For smaller-scale prints, the narrower 'ppsnap4small.stl' solves the biggest tolerance issues for otherwise tight-fitting joints. 
Hardware:
Cables are usually braided fishing line, with zero stretch being preferable. I use 250lb, but you could get away with a lot less, especially for a kid.
For a 160% print, I used:
6 x #10/24 3/8" set screws as cable anchors. Five for the flexors and one more to bundle the extensors.
2 x 1/4"-20 3/4" flat head cap screws and 2 matching nylon lock nuts for the wrist hinge.
2 x #4 3/4" pan head screws for the pivot cover.
4 x #6 1" pan head screws to hold the cable guide onto the unipalm 20 x #6 5/8" truss head screws to hold a leather "shoe" in place, to fit the fingerless palm of the user.

Here's a hardware list for a print at a scale of 100%
Wrist hinge: (2) 8-32 x 5/8" flat head hex screws; (2) 8-32 nylon lock nuts
Cable anchors: (6) set screws 6-32 x 1/4
Cable guide: (4) pan head sheet metal screws #4 x 5/8
Palm leather mount: (16-20) truss head sheet metal screws #4 x 3/8
Nylon webbing can be used to make straps, with rectangular rings and Velcro or double d-rings as a closure over the forearm.