Originally Posted by
Spandex_fairy
Thanks, but I I found that diagram previously. I don't see where in the instructions that it says a regular expander plug can be used. The internal shape of the steer tube is not round; it's more like a rounded triangle. It comes with a propriety plug; it's unique to this specific bike.
Than there may have been a misunderstanding. Call them back or go to a Trek dealer. Its possible they are out of stock, but the part must exist.