I made this for mounting a rectangular digital hygrometer in the SUNLU filament dryer box.

You can use the straight holder for mounting it on the bottom filament exit hole or the 45 degree one on the top filament exit hole.

Picking between hex or round nuts is only for aesthetics. I mounted a round nut butted up against the bolt head outside of the enclosure just for added strength.

Print nuts and bolt at 0.1mm layer height, everything else is OK at 0.2mm. 100% infill for bolt. 20% infill for everything else was fine for me.

I also included a desiccant holder to mount to the same bolt, as a bonus. The size is based on the particular desiccant packets I have and the amount I wanted to place inside.