jhoop31 (Jason) & C III fan...
Hello Jason.
That would be an aftermarket fan that you describe.
And Bill is correct on both accounts; by the 50's & 60's, MOST, Genuine Kirby parts started to have part numbers on them; secondly, those 'circles' on the back of the metal fans are/were for balancing.
Another thing, is that prior to the two (2) plastic fan versions, (Lexan ['80~'96] & Amodel ['96~present]), the Genuine Kirby fans were/are a one-piece fan assembly. Component fans did not start 'til the Lexan fan.
If you have further questions about this or other Kirby questions, shoot me an email & I will provide you all of my contact info. And, if you are after Kirby parts, keep me in mind next time as a source for your Genuine Kirby wants & needs. I'm sure I will be able to save you substantially.
I carry only Genuine Kirby parts.
Cheers & hagn/d all,
Bill
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