Johann's original Extruder uses stepper motor with Planetary Gearbox (5:1 ratio). It is an excellent minimalist design which works reliably.
This is a modified version which uses standard NEMA17 which is good enough to do the job.
Parts list :
1pc NEMA 17 Stepper Motor
1pc Drive Gear (11mm diameter)
1pc 625ZZ Bearing
1pc Push fit connector (M5 thread)
1pc M5 x 16mm cap screw
1pc M5 Nut
3pcs M3 x 10mm cap screw
Assemble the extruder based on the pictures.