This is slightly over engineered modular Filament Rack made out of 3-4 parts. In my version it uses ½ inch EMT conduit (about $5 each @ Home Depot) but you're not limited to EMT conduits, I've added a bunch of different versions for different holes that you can put pretty much any round stick within reason.

The good thing about this rack is that you can make it any width you want to fit into any space; you're not restricted by 3d printed parts that are set width; just cut the pipe into whatever length you want and slide it in.  It is also pretty efficient overall; a 3 floor double section of the rack excluding cost of EMT will use about 27 grams of filament per spool (1.6kg total / holds 60 spools)

I used EMT conduit in mine because it's strong and doesn't bend easily and I've had it standing for over 2 years now without any issues; I even printed it in standard PLA.

You can go as many levels as you want, just print extra set of “Middle Point” and “Riser” per level.

These are the included sizes of holes so far:

• 11mm (0.43 inch)
• 18.7mm (0.74 inch) - For ½ inch EMT
• 20mm (0.79 inch)
• 21.32mm (0.84 inch)
• 23.5mm (0.93 inch)
• 24.5mm (0.96 inch)
• 26.4mm (1.03 inch)
• 28mm (1.1 inch)
• 29mm (1.14 inch)
• 30mm (1.18 inch)
• 31mm (1.22 inch)
• 32mm (1.26 inch)
• 33mm (1.3 inch)
• 34mm (1.34 inch) 

Make sure to use part that has at least 1mm bigger hole than what you want to put in it.  For example if your pipe is 30mm use 31mm version files.  If you're not sure which hole you need I added print profile with small samples of all of the holes; print one of them and see if it works.

If there is no print profile for the size you want click on “Download STL / CAD files” and download the .zip.

• There are also two longer Riser parts in there that you can use to have more space between spools for filament boxes or other things

I'm including STEP files for 18.7mm version so you can make the holes bigger yourself if you know how to.  Also, if you're printing one of the larger hole versions increase wall count / infill on “Middle Point” and “Top” parts as they become weaker the bigger the holes are.

Edits:

• November 12, 2024 : Added two versions of wall bracket if you need more stability at higher levels, it clips onto Riser part and you can either put screws in the wall or use double sided tape.  I've added print profile for them.
• December 4, 2024: Added A1 mini compatible version of the base part; place it at 45degree angle and it will fit the build plate.  You also have to print riser part at an angle with some supports.
• July 13, 2025: Added tags with labels for labeling your filament rolls:
• 
• May 4, 2026: I made the holes customizable, click the customize button, select hole size you desire (from 1-35mm), click generate and then download it.  Print the plate twice and you will have the same rack as the last photo in the description (1 section 3 floors tall; good for 30+ spools)  I'm leaving all original files of different hole sizes in here, they worked fine for many people so far so they could still be useful.  Oh and after you generate add some brims for risers, they're tall and don't have a lot of contact points with the plate.   Let me know if you want any other parts customizable besides hole sizes.