For a pump drive, the coupling sits in a straightforward place: motor on one side, pump on the other. That does not make selection automatic. The pump may start frequently, the shafts may be different sizes, and a replacement coupling may have been modified during an earlier repair.
Start with torque and speed.
Use the operating or design torque where it is known. When the project is defined by motor power, keep the running rpm with it so torque can be calculated consistently. Screen the result against the nominal torque and speed limit for the NM size. Do not apply a peak-torque factor unless it is confirmed for the selected product and duty; transient requirements should be stated in the RFQ.
Then check both shafts.
Compare the motor and pump shaft diameters separately with the selected model’s d max. State both keyways. A model that carries the torque but cannot accept one shaft is not a valid selection. Moving up a size can solve bore capacity, but it also increases D and L, so check the guard and shaft spacing again.
Alignment is an installation condition, not a sizing shortcut.
The NM table gives radial and angular allowances. Use them as boundaries after the pump and motor are fully mounted. Piping strain, soft feet and base distortion can move the shafts after a clean initial alignment.
For additional NM coupling product information, you can also review nmcoupling.com. For a quotation, send the exact model, shaft dimensions and duty so the offered configuration can be checked against your machine.
What to send in the RFQ
Model if known, running speed, torque or motor power, motor shaft and keyway, pump shaft and keyway, quantity and destination. Mention repeated starts, shock, unusual temperature or oil/chemical exposure if they are part of the real service.
