CHECK OUT MY NEW AND IMPROVED DESIGN, THAT IS EASIER TO ADJUST IN WIDTH USING A SCREW
This is a filament spool mount holder. It works with 4 bearings. Inner bearings diameter should be 8 mm. The knob is made 8.05 mm, so its a press fitting. I had to sand it down a little myself for a good fit.
It has a custom width, so it should fit most spools.
It is quite sturdy, and has a good slide, with the right amount of friction. I recommend fixing an elastic to push the two holders together.
UPDATE: I've made a loop around for fixing the elastic, since the stick is not very good (Too tiny). I have not yet printed this, so ill leave both files up.
UPDATE2: I've added a new rail with Ø10mm holes for fixing neodymium magnets into. I've used 2 screws into the box where my 3D-print is. This allows for a much better fixture and easy removal when changing filament or when the spool gets in the way.