Well, having not seen these brushes yet myself, I can possibly give a lead out that may prove useful. The place I work for, likes to use old antiquated equipment they buy cheap @ auction, in their maintenance department. So, being one of the plant electricians we have to find sources for these golden oldies. For a vast variety of brushes on our old DC motors and motorized welders we have found a company called Helwig Carbon. pretty much you tell them what you have, give them some measurements if needed and they usually have it. Might prove useful for the fan motors too, I have one I need to someday rebuild, but have yet to figure out how to get it apart,lol.

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Chris
64 190D R.I.P.
80 240D W/617 engine -for sale
82 240D -for sale