Stepper Motor NEMA^ Sizes

NEMA is "National Electrical Manufacturers Association" and their standard for motor mounts is commonly used in the industry to ensure that replacement parts will fit and be readily available, and that motors from different mfgs will be interchangeable. The NEMA number is related to the diameter of the motor times 10. So a NEMA 23 motor is 2.3 inches around or down the side.

Please note: These figures are put together from multiple sources and may or may not be right. Please let us know if there is an error.

Dimension in Inches (mm)	NEMA Motor Mounting Dimensions
	NEMA 8	NEMA 11	NEMA 14	NEMA 17	NEMA 23	NEMA 34	NEMA 42
Motor Size (DD)	~0.8 (20.32)	~1.1 (27.9)	~1.4 (35.6)	~1.7 (43.2)	~2.3 (58.4)	~3.4 (86.4)	~4.2 (106.7)
a: Bolt Hole Distance (square)	0.630 (16)	0.905 (23)	1.024 (26)	1.220 (31)	1.854 (47.14)	2.744 (69.7)	3.500 (88.9)
b: Motor Shaft Diameter	0.157 (4)	0.197 (5)	0.197 (5)	0.197 (5)	0.250 (6.35)	0.375 (9.5)	0.625 (16)
c: Motor Shaft Length (max)				0.945	0.810	1.250	1.380
d: Pilot Diameter	0.590 (15)	0.866 (22)	0.866 (22)	0.866 (22)	1.500 (38.1)	2.875 (73)	2.186
e: Pilot Depth (max)	0.059 (1.5)	0.079 (2)	0.079 (2)	0.079 (2)	0.062 (1.6)	0.062 (1.6)	0.062 (1.6)
f: Bolt Hole Circle Diameter	0.891 (22.6)	1.280 (32.5)	1.448 (36.8)	1.725	2.625	3.875	4.950
g: Bolt Hole Size	0.118 (3)	0.157 (4)	0.157 (4)	4-40 UNC	0.195 (5)	0.218 (5.5)	0.281

Thanks to Neil (PICDude) for these excellent pictures!

The primary NEMA number specifies the position and size of the mounting face as shown in the table above. The full NEMA standard also describes other features of the motor. The full NEMA description of a stepper motor is written as:
NEMA DDMMLLL-CCCIVVVSSSW, where:

• DD is diameter (inches x 10). For square stepper motors, the length of a side is used instead of the diameter.
• MM is mount type code (inches x 10), include none, one or both of these letter codes
  • "C" if there are holes tapped in the face of the motor
  • "D" If there is a flange on the back end of the motor with slots missed for bolts to pass through
• LLL is length (inches x 10),
  the "-" at this point separates mounting info from electric characteristics.
• CCC is phase current (amps x 10),
• I is insulation class and defines the maximum allowable operating temperature
  • Class A is 221'F
  • Class B is 266'F
  • Class F is 311'F
  • Class H is 356'F
• VVV is phase voltage (rating x 10),
• SSS steps per revolution,
• W is a winding code.
  • A is two wires,
  • B is 3 wires,
  • C is 4 wires,
  • D is 5 wires,
  • E is 6 wires,
  • F is 8 wires

For example: a 3.4" diameter stepper motor with a flange that is 1.6 inches long, has a phase current of 1.2 Amps, class B insulation, 5.3 phase voltage, 200 steps per revolution, and 8 wires is: NEMA 34D016-012B053200F

See also:

• http://www.nema.org/stds/mg1.cfm only $305
• http://reprap.org/wiki/NEMA_Motor
• http://www.numberfactory.com/NEMA%20Motor%20Dimensions.htm

Comments:

• On this page (stepping motor dimensions)the chart shows "common" or NEMA specified shaft diameters. But in reality there are wide variations in shaft diameters. I know because I have many of them. Perhaps a note or comment to this effect would help someone.
• f, the bolt hole circle diameter, is simply a times 1.414 (the square root of 2). So NEMA 8, 11 and 14 diameters are 0.891, 1.280 and 1.448, respectively.
• Nema 42 motor shaft diameter seems to be .750" on the motors I've seen.

Questions:

• kashivar@gmail.com asks:

  I have a query. I have a stepper motor square of 4.2 inches and length of approx. 6 inches. It has 4 (Four) wires, bipolar. apart from this I have no other information. I may be able to measure the coil resistance at the most. how do i determine the working voltage, current and watts? I need to choose a suitable drive for the motor.

  James Newton of MassMind replies: See wiring to work out which wire is which. As to the rest, I really don't know.