For my CNC router / mill project I have decided on NEMA 23 hybrid "closed loop" stepper motors. I'm confused. The first page on Ebay I found 10 different torque / holding torque ratings for the NEMA 23 closed loop motors: 156oz 170oz 262oz 285oz 298oz 312oz 314oz 315oz 370oz 428oz. How, what and why? What's up with that? I know what torque and holding torque is but how can the same size motor have so many different torque ratings?