The provided STL file contains the four pieces that make the extruder. Besides that, you will need:
a piece of M5 rod, 62mm long.
one nut (locking-nut is best, but a drop of super-glue worked for mine)
two 625 bearings
a drive gear
a 608 bearing and 20mm M8 rod for the idler.
a j-head hotend
two 30mm M3 screws and nuts for fixing the hotend.
Please note the small gear is for a shaft with a flat. It will pressure fit without needing grub screw. If your motor does not have a flat you will need to drill to size the gear bore so it becomes round.