EMA stands for National Electrical Manufacturers Association

Both Stepper motors and Servo motors are manufactured in various Nema sizes and each with different stack sizes, they are measured by flange sizes as:

nema 6 stepper motor
nema 11 stepper motor
NEMA 23 2.3 inch flange
NEMA 34 3.4 inch flange
NEMA 42 4.2 inch flange
nema 52 stepper motor


Flange size is dimension of the motor flange while the depth or height can vary from single stack to 3 stack in each of the above size. More stacks in same flange size add to the power of motor but will heat more due to more heat generated for the same frame size.

Other way of increasing power or torque to the motor is of course increasing the size as mentioned in above table, but be cautioned that bigger the motor, slower it will run due to more detent torque. (detent torque is the stickiness of motor with no current flowing and this need to be overcome and subtracted from the overall torque produced by the stepper motor)

So it pays to optimize (use the smallest required) motor for a particular application and use the better (micro stepping, bipolar) drive that have features like antiresonance and optimum driving waveform to extract most from the motor at all speeds with well matched driving voltage and current.