I uploaded the .STL files and the .3MF files sliced on Cura if you want to use my printing settings.

To make it you need:

3 printed parts
1 hardwood dowel. 1/2 in. x 48 in. You just need 29cm.
2 #8 1/2in screws or similar..
0 to 10 12mm x 2mm magnets. The amount is up to you and it'll define how strongly the paper towel stand will be held on a metal surface.
Assembling:
After you've printed the base, knob and connector and the dowel sawed to the required length (29cm), insert the connector on the dowel and use one screw to secure it.
Insert the other end of the dowel on the base and use the second screw to secure it. Glue as many magnets as you like. Do it one at a time until you are satisfied.
Put the paper towel roll on it's place and secure it screwing the knob on the top.

[UPDATE]: V2 of knob and connector uploaded. It has less threads, making it easier and faster to remove the knob when needed. The connector also has at the ends a few mm with no threads at all. The top part is intended to make it easier to align the knob when putting it in place and at the bottom is to leave some space to grab with your hand if the knob it to tight. NOT TESTED YET. If you test the version 2, please let me know the results.

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