Prop Decoder

[FYN409]

Ok, I am considering changing the prop on my Sorrento 25. Looking at the charts on Sea Rays site it recommends a 15.5x18. I checked the numbers on my prop and this is what I found 48-78118-15 (the last 8 could be a 6 but it is hard to tell). I have done some searching and found that number on the net, but nothing that states what the specs are. Anyone know how to decode that number? I would like to see how close that is to the original spec.

Thanks,
Ryan