> Can you show me the federal code that includes number of customers?
I never mentioned ”number of customers”. The relevant law surrounding monopolies is the Clayton antitrust act of 1914
https://www.law.cornell.edu/uscode/text/15/18
What is and isn’t a monopoly is of course decided on a case by case basis - as it should. There is no law saying that 80% market share is necesssarily a monopoly or that 20% is so low it can’t be blocked.
> Do you think a small mom and pop store in a rural captured market couldn't price fix?
Not sure how it’s relevant but they can of course haves local monopoly - but afaik in the US such local monopolies aren’t subject to regulation.