1. Determine Torque and Select Size
This is the most critical step. The coupling must be sized to handle your application’s torque without failing.

• Calculate Application Torque: Use standard formulas based on motor power (kW or HP) and speed (RPM).

• Apply a Service Factor: Multiply your calculated torque by a service factor based on the driven equipment (e.g., 1.5 for pumps, 2.0 for conveyors, 2.5+ for crushers). This accounts for shock loads and operational harshness.

• Check Coupling Ratings: Select an NM coupling size where its Rated Torque is greater than your calculated torque (with service factor). The manufacturer’s catalog will provide a torque table for different sizes (e.g., NM05, NM07, NM10).

2. Define Shaft Dimensions and Bore Type

• Shaft Diameters: Accurately measure the diameters of both the motor and driven machine shafts.

• Bore and Keyway: NM couplings typically come with parallel bores and keyways. Ensure the chosen coupling size can accommodate your shaft diameters. Custom boring is often available from manufacturers.

3. Assess Operational Limits

• Maximum Speed (RPM): Ensure your system’s maximum operating speed does not exceed the coupling’s maximum speed rating.

• Misalignment Capacity: NM couplings are excellent for compensating angular and parallel misalignment. However, you must ensure the expected misalignment in your system is within the coupling’s specified limits to prevent premature wear of the rubber element.

4. Evaluate the Operating Environment
The rubber (elastomer) element is sensitive to its surroundings.

• Temperature: Standard NBR rubber works in a range of approximately -30°C to +80°C. For higher temperatures or outdoor UV exposure, materials like EPDM may be required.

• Oils & Chemicals: Exposure to oils, solvents, or ozone can degrade standard rubber. Choose a specialized elastomer material if present.

Quick Selection Checklist

Why Choose an NM Coupling?
Choose an NM-style coupling for applications requiring good vibration damping, electrical insulation, and moderate misalignment compensation. They are a robust, maintenance-free (no lubrication) solution ideal for pumps, fans, compressors, and conveyors.

Final Tip: Always refer to the specific manufacturer’s sizing guide and technical data. Reputable suppliers provide detailed tables that match coupling size to torque, speed, and bore capacity. For complex applications, consult directly with the supplier’s engineer.