NEMA 17 Stepper motor
A NEMA 17 stepper motor is a stepper motor with a 1.7 x 1.7 inch (42.3 x 42.3 mm) faceplate. The NEMA 17 is larger and generally heavier than for example a NEMA 14, but this also means it has more room to put a higher torque. However, its size is only a coarse indication of its power.
Length (L) isn't part of the NEMA 17 standard. Various lengths exist, typically maximum torque (and weight) increases with motor length.
Common Stepper Motor Models
The most commonly used stepper motors in RepRap based 3D printers are the Kysan 1124090/42BYGH4803, the Rattm 17HS8401 or Wantai 42BYGHW609.
However motors close to NEMA 17 size, rated 1.5 A to 1.8 A or less, 1-4 volts, 3 to 8 mH, 44 Ncm (0.44 Nm, 62 oz.in) or more of torque, 1.8 or 0.9 degrees per step (200/400 steps/rev respectively) can also work.