The original spool holder with a flat bottom is excellent.
Thank you JohnSL for making it!
I made the remix, because the original is a bit short and my spool was pulled off of it one night during printing. The yellow ones are the original ones, and the black ones are my remix.
I extended the rail from 80mm to 100mm length, for stability and lowering the centre of gravity. Because the extra distance between ball bearings, the spool goes a bit deeper into the channel of the holder. That is why i cut out a circular shape from the walls, so a full spool of filament won't touch the holder and rub against it.
Please let me know if you have any troubles with it, so i can get you sorted out with an improved model. Maybe use a different cutout radius.
Also, because of the distance between walls, i made some M8 washers to center the ball-bearing in the holder channel. It makes a lot of difference even with the original design. I am using 8 pieces per screw. Two outside and two on the inside, on each side of the ball bearing. That way it is centred, and the edge of the spool cannot jam in-between the wall and the bearing. See the photos.
I'm using M8x30mm screws, that's why they are a bit longer.