Wrist Double Joint

A double-revolute joint which serves as a wrist joint.
Consists of three parts; Alpha, Beta and an adaptor to attach this wrist joint to a hand, which is available in a separate upload.

The 'Alpha' wrist part is designed to slot over the end of 20x20 aluminium extrusion.

Of course, if you have CAD software like Fusion 360, you can modify the .STL files of both these parts so that they will fit whatever you like.

The 3DP nut and bolt in this joint have been adapted from

https://www.thingiverse.com/thing:193647

by mike_mattala.

However, they are pretty weak. Especially at this small scale if only printing in PLA.
Don't over-tighten or the top will snap off the bolt. As you can see in the photos, I have already had to replace one of the PLA wrist bolts with a steel one because the end snapped off.

It's a good idea to use 35-45% infill at 0.1mm fine resolution for the main parts of this joint, then increase the infill percentage to maximum 100% for the nut and bo