What does the third digit in a motor frame size specify?

• A. Shaft height
• B. Shaft diameter
• C. Number of motor poles
• D. Distance between the foot holes nearest the shaft and the opposite drive-end foot holes

Answer: (D)

In motor frame sizing, the digits describe the physical mounting footprint of the housing. The third digit specifically defines the distance between the mounting feet closest to the shaft and the feet on the opposite drive-end side. This foot-to-foot spacing is what determines whether the motor will fit a base or equipment with a matching mounting pattern. Shaft height and shaft diameter are fixed mechanical features listed elsewhere, not by this digit, and the number of poles is an electrical characteristic that affects speed and torque, not the frame’s mounting spacing.