That's the problem, I'm buying one that the original eye has broken. I need the original eye spread so I can replace it. Don't want to tow it 200 miles without a bow eye.
I take it you are buying the boat from someone 200 miles away and therefore don't have easy access to it. Can you have the seller take some measurements, at least the distance between the holes? I would guess it has a 3/8" eye. I got the following the EPCO website, but as SB said, this should be standard for the industry.
Standard dimensions between the legs of the bow & stern eyes:
3/8" Sizes 1-1/32" ID & 1-13/32" CTC & 1-25/32" OD ± 1/64" Tolerances
7/16" Sizes 1-1/2" ID & 1-15/16" CTC & 2-3/8" OD ± 1/64" Tolerances
1/2" Sizes 1-5/16" ID & 1-13/16" CTC & 2-5/16" OD ± 1/64" Tolerances
5/8" Sizes 1-1/4" ID & 1-7/8" CTC & 2-1/2" OD ± 1/64" Tolerances
Since you don't know how long the old one was, you would probably be better off getting a fairly long one, since too short will do you no good.
edit: if the seller can't get the measurement for you, you can buy 2 or 3 sizes to take with you. Keep the receipt and return what you don't use.