This is a corner for a frame made for 1/2" tubes to can make a termal isolation enclosure frame for your 3D printer. The holes are slightly oversized so you can glue the tubes in. You can make 8 of these for your cube, then cut the tubes to fit your printer. The cover can be made from thin roof isolation foam (https://www.insulation4less.com/) or car sunshades cut to size and sewn.

You can complement the enclosure with a thermometer corner bracket

https://www.thingiverse.com/thing:5567681

and a fan frame that holds on to the 1/2" tube.

https://www.thingiverse.com/thing:5575821