Hmmm?, a double thread would be like slipping two springs into each other from the side, two parralel channels for the water to run up. you could hve three or more but i't be harder the more you had.
Get a pencil and two bits of string, then wrap them around the pencil without them overlaping, think of them as the water channels.
PS, I though of three at first cause thats the height (in threads) of the inlet.
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