Thrust for Mercury Thruster Plus

[Gone Fishin']

I bought a Mercury Thruster Plus a couple years ago, and I forgot what the thrust was for it. I want to think it was 40lb, but I did a quick google for it and only found 28lb for it that other people owned. I can't read the serial number on it so I can't look it up either. Would anyone happen to know whether it's more likely to be 28lb than 40lb thrust? I know I'm not giving that much for anyone to work with here, but I thought I'd just ask. Thanks.