Is anyone familiar with a balancing specification (Class III M5B)? I balanced a fan in our shop stand this past week and the customer specified this saying it was an engineering spec. We use an IRD 290 and it has several selections but M5B is not one of them. The fan runs 3550 RPM and weights 225 lb. I used 4W/N and had to get it down to less than .5 gram correction to be in tolerance and the customer was ok with this. I was hoping someone has knowledge of this spec and is there a "G" spec that would be equivalent?

Thanks,
Ronnie Lynn

I never heard that term.

The term "Engineering Specification" does not usually refer to industry standard documents. Is it possible the term "Engineering Specification" refers to a spec prepared by the Engineering Department of his company? In that case you have to ask that particular company.

Thanks Pete. Just thought it might be a specification that I hadn't heard of. The fan came to us through another vendor, one that does metal fabication, so I don't know which industry it belongs to. I know they accepted 4W/N so that must meet or exceed their specification. G2.5 satisfies the majority of our balance work and 4W/N has always been the tightest tolerance we deal with.

Thanks,
Ronnie

The balance tolerance of API (4W/N) is equivalent to G0.66. Sure the customers are very happy with that. They got more for the same price.

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