Fans and blowers often run for long periods, so a small alignment or balance issue can become a persistent vibration problem. The coupling can add damping, but it should not be used to mask a poor rotor, soft base or misaligned shafts.
Check the high-speed end of the range carefully.
Running speed is a direct model limit. NM50 through NM168 are rated at 3000 rpm, while NM194 and NM214 are rated at 1500 rpm. If a larger bore pushes you toward the two largest sizes, re-check speed before treating the bore solution as final.
Leave room to inspect the element.
Fan guards and compact skid layouts can make elastomer inspection awkward. During design, confirm that maintenance staff can reach the coupling, verify the hub condition and replace the ring without creating a new alignment error. A coupling that is technically sized but impossible to service is still a poor package decision.
Large shaft, high speed?
That combination deserves a deliberate review because bore demand and speed limit can pull model choice in opposite directions.
