based on:
G-Clamp fully printable by joehann on Thingiverse: https://www.thingiverse.com/thing:1673030
(used his threads directly)

clamp designed with a fitting sleeve to compensate for printing orientation or any other inaccuracy, makes it stronger and gives it a perfectly tight fit.

the sleeve is also extremely simple to design and quick to print, so it can easily be adapted to any other diameter as needed.