Thick shell (2mm) to make strong sidewalls and threads.
The #8 screw holes on the socket are blind (don't go quite all the way through) in the OpenSCAD model and hence in the STL file, but Cura thought the remaining thickness was too small and left the hole open all the way through. The hole could be lengthened in the OpenSCAD model to make the STL file match what was actually printed.
Use 1" #8 flat-head wood screws to attach the socket to the broom head.
Use 2" #9 flat-head deck screws to attach the guide to the broom head.
Pilot holes in the broom head are needed to avoid splitting the wood (5/64" for #8 screws, 3/32" for #9 screws).