Recently bought a 1992 40 hp Mercury 2stroke, 4 cylinder outboard motor. Started looking at spare props, I have been told the came with fixed hub and replacable hub props, how do I tell the difference?? Took the current prop off, poked, pushed, pulled but not finding a hub that comes out. Is this a fixed hub? Looking for an education on identifying these props. After over 50 years of boating never saw a replacable hub, I dont think I have anyway