Agile Spool Adapter (20mm)

I needed a reliable spool adapter to mount standard 1Kg spools to the [20mm pipe spool mount I designed](https://www.thingiverse.com/thing:3095951) for my Geeetech I3 Pro B.

I tried a few designs I found here on Thingiverse, but none was satisfactory: some weren't reliable, slipping out of the spools at the most inappropriate time, others were too brittle, breaking apart after one single use.

Here is my solution, with the *Full* version including grab slots for fingers as I thought it woul