Neu motor Ratings

[BrianG]

All the motor specs do mean something. For example, let's take a 1521 1.5d/f motor.

15 - Relates to the rotor diameter. May be the diameter of the rotor in mm, but not sure.
21 - Relates to the rotor or motor length. Larger numbers means a longer motor.
1.5 - The number of turns
d - The coil configuration: d=delta/triangle. y=wye/star
f - f=finned can. No value means smooth can (no fins)

Neu's website lists all the specs for the various motors, or you could use the chart at my site to make it easier to compare against other manufacturers motors.