I've designed this simple wall mounted bracket to help me organise all my spools.

There are two versions. One metric which works with a standard 18mm wooden dowel and one imperial which works with standard 3/4inch dowel. Both of those dowels are standard issue in any hardware store.

You mount it using M4 screw/bolt.

I would suggest printing an extra bracket every 7th spool, so roughly every 58cm.

I mounted my bracket on the side of Ikea Alex cabinet and it happily takes 7 spools with no issues. But if it was longer I'd probably put another bracket in the middle to bear the weight.

You can secure the dowel with zip tie or just wrap some tape around it on the inside of the bracket on both ends so it doesnt come out.

I printed mine using Sunlu PLA+ with 5 walls, top and bottoms and 15% gyroid. If you use PETG or ABS you could probably drop those numbers down.