Use a bolt and nut or for extra stability and strength if you need to hulk on the paper roll, use a threaded bar all the way through with a nut on each side.

For easy assemble/disassemble, use these knobs with the hardware:

Print with 4+ walls, adn 45%+ infill for strength. Here i printed in PLA+, but you can choose whatever filament you believe to be adequate.

Update 260302: Changed mounting holes to keyhole shape for easier hanging/installing