Hole in the top part may need cleaning with a drill bit. Pre-modeled 8mm and 10mm holes.
Hammer the pin into the bottom part so the whole thing won't rotate inside.
3mm holes pre-modeled to screw the halves together with whatever screws you find. I used M3x20. Or just glue/fuse/melt them together if you don't plan to take the extension rod out later.
The top part is made so thick in assumption that it's printed from ABS/ASA/HIPS, for the purpose of hot-tightening nozzles.
The author hasn't provided the model origin yet.