Needed to remove an octagonal nut in a tight space, for an unknown Shower Cartridge replacement. Couldnt find an octagonal box spanner anywhere so Bought a standard 32mm box spanner (sink backnut spanner) and designed this to be an interface between the two.

Perhaps it might help someone else.

I printed it upside down with supports as the octagonal end would end up too squished in the bottom layers for me, stopping the thing from grabbing the nut properly.