Maximum permissible limit for an investor to purchase shares in a company?

Hi everyone,

I wanted to know if there is any limit on a shareholder to acquire shares of a US-listed company. For example, is there a percentage limit of total shares that a shareholder (including the original company founder) can purchase from the open market before any rules or limits trigger in? If there are such rules, what are they?

From where I am based, a shareholder cannot acquire more than 5% of the total share base of a company in a particular year. If the shareholder buys more than 5%, then he/she must compulsorily make an offer for at least 26% of the total shareholder base (if the offer is not subscribed entirely, that is fine, but the shareholder has to make the offer).

What equivalent rules exist for the US markets? Any help would be appreciated.

Thanks.