Spool Adapter for Filament Shelf

I love this Filament Shelf (thing 2253244) by asteinmark. As it happens, I put my shelf directly above my 3D printer, so I wanted a way to spool filament to the printer directly off of the shelf. I made this adapter that enables exactly that.

(Note to choose the correct version of the side rails STL to match whether your shelf is based on *asteinmark*'s version D or version C. Use **shelf_mountable_spool_holder_for_Version_C.stl** if you have Version C, otherwise use **shelf_mountable_spool_holder_mashup_v2.stl**, which is compatible with Version D. Thanks to yetisnack for catching that both versions are needed.)

You will need 4 standard skate bearings, and 4 8mm x 35mm bolts (with nuts), and 4 medium-size zip-ties.

Assembly instructions:

* Print 2 each of the appropriate side rails (see note above), and 4 each of the bearing adapters (new-bearing-adapters.stl). 20% fill seems to be plenty strong.
* For each side rail:
* Bolt two skate bearings into the two holes provide