A spool holder designed to fit onto the 20mm profile of 2020, 2040, 2060 and other such aluminum extrusions. The arm fits over an into the extrusion and the retention plate goes on the other side to sandwich the extrusion. Use M5 screws and nuts of the appropriate length for the extrusion you are attaching to with a minimum of 1.2 mm for 2020, 3.2 mm for 2040, and so on.
For the axle I used a piece of wood dowel I had lying around, wrapped with a bit of duct tape to get it to roughly 7.8mm diameter. I then put on some 8mm bearing which the spool rolls on. You can use what you want here as long as it is solid enough to hold your spool.
This spool holder is rigid yet light due to the framing. The way it clamps onto the aluminum extrusion is very solid. The top is open to make it easy place and take out the axle.
The STL are made so the objects are lying flat on the bed when printing. Print this way for best results. You will need to print two of each for a complete holder but I recommend you print them one set at a time. This way if your printer tolerances are off and your part won't fit onto your printer you can adjust and note have wasted as much plastic.
Use 4 screws and nuts to secure the parts together. It is normal for the center tooth on each part to have a little resistance as you push the part on, this is part of what makes a tight fit. It is not normal for the part not to fitting all the way down into the extrusion because the outside legs are too tight. If this is the case for you just size up 1% and try again.