This is my 3d modeled version of a dual wheel Wartenberg Pinwheel.
See https://en.wikipedia.org/wiki/Wartenberg_wheel
These make for excellent back rollers. ;)
This whole thing can be printed mostly without supports. Depending on how well your printer does with bridging the slot in the body for the handle could potentially be problematic. Experiment to see what works best for your printer.

Files:

@all parts.stl:
This is a single STL file with all of the parts. Mainly for reference or tinkering or etc.

1-8 washer.stl:
This goes on the shaft in between the 2 rollers.

1-16 washer.stl:
Print 2 of these. They go between the body and the outside of each roller.

body.stl:
The main body that holds the rollers and shaft

handle:
well....it's the handle! lol

roller.stl:
print 2 of these

shaft.stl:
shaft, axle, or whatever you want to call it.

A couple of quick notes:
The shaft is meant to be a tight fit into the body. you will most likely need to sand a few thousands off of the shaft (or the inside of the holes). Just do this a little bit at a time until it slides in but with some effort so it doesn't fall out. I have also provide screw holes to secure the shaft to the body if needed for any reason.

There are 2 screw holes to attach the handle to the body. The holes in the handle are not threaded, use self tapping screws.

If you make one of these please use the "I Made One" feature and upload a picture along with your printer info and print settings used!