Vintage metal dual bladed boat propeller... probably from an outboard motor. It has worn old industrial green paint It's aluminum I think, non-magnetic and certainly not brass.
This propeller measures approximately 8" in diameter and 1.875" across (at the large end), the tapered spline. The spline is 18 teeth around. I don't know what motor it fits, but it would be great for steampunk decor projects or upcycled and repurposed.