SC8UU compatible linear bushing with M4 thread

A SC8UU compatible linear bearing with M4 threads. No nuts required. You need a small nozzle (I used 0.3mm nozzle and 0.2mm layer height) and low layer height to be able to print the M4 thread (M4: 0.7mm pitch, 0.6mm groove depth, see photo) and the inner fins. Should the thread wear out a nut can still be conveniently used.

The good bushing shape is adapted from the LM8UU shape by FlyingMashedPotatoes (http://www.thingiverse.com/thing:631285) which really has some spring functionality.

- Version 1 has a smooth running thread which might __wear off__ easily.
- Version 2 has a quite tight thread which will not wear but needs some force during screwing in.
- Version 3 allows for tilting in one direction to compensate bent rods (see colorful picture).
- A 'short' version is also made
- A long sc8wuu version added
- A stiffer version (for example for x-axis) was added

Drop a message if you encounter any problems or have suggestions.

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