Well, if it looks like a duck, has a bill and webbed feet, it probably is a duck! It has 15 splines and has the number 19 stamped in the hub. It is bronze and Mercs did at one time have 2 blade props. It is probably a Mercury or aftermarket Michigan 2 blade prop for the larger engines like 100 or 115 (1000 or 1150). Probably a 13 X 19. Since diameter would be nominal simply measure across both blades and don't be surprised if it is different from 13 inch. It may have been repaired; there appears to be a prop repair shop letter stamped in the hub.
You can call Mercury customer service and get full information on the prop from the numbers on the hub.
