The stock spool holder that comes with the x1 isn't the greatest.  For me it caused just a bit too much resistance, pulling the extruder up ever so slightly and thus layer variation.  

So I made this with two options that can be swapped out on the main bracket.

-1. A spool holder assembly that uses skateboard bearings for super low resistance. - Possible that the resistance could be so low that the spool may unwind way easier than one would like, but i have had no issues yet.

-2. And a simpler basic holder that offers a slight bit of resistance that is still a big improvement over the stock one.

The 2 bearings needed should have an 8mm inside diameter and 22mm outside.

To mount this you could get by with using the existing hardware from the old holder and just mount on the backside, but it is more stable if you mount on both sides.  I recommend using 5mm tnuts with 10mm long screws.

Of course this could also be used on other 20mm extrusion machines.