The newer XL tower kits fixed this issue, but if you have an older tower kit with 4 casters, it only really fits the included spool. Instead of rewinding filament or only ordering from brands with the exact spool size, just print 2 of these spool expanders to allow any size spool to sit on the tower.
Printing recommendation - This is a tall object to print, your z calibration might be a little off since small amounts will multiple with 180 layers. This takes about 1 hr to print. Use a piece of paper and measure out what will fit your tower, then as it gets close, check to see if it hits your mark. Once it does, hit stop. The design is for 75mm.
I included multiple versions, a tight one that might need filing/sanding to get it to fit or a loose one that will easily slide over. Based on how calibrated your printer is, I would recommended just using the loose as it doesn't really matter.