Again remix of: kriswillcode
Got inspired by th1nzz better grip
Just found out there is already another middle piece which is wider by jbwebst

Hacked together with blender booleans and fixed broken stl by netfabb(through slic3r).

This version is printable without supports (notches and holes not mixed on one side.)

Use the 6mm holed version with an axle, for example a wooden chopstick.

Use ReallySoftSpring with PLA.

Note: I could not get rid of all the spacing between the parts with some quick postprocessing.