It's 15 spline I got it in a job lot of props at the time I was after some mariner/merc props and this came with them it's never been fitted so all I know is it should fit yamaha outboards 150hp+
It will fit smaller engines too, my f70 yam has a 15 inch spline as did my Suzuki 90. The same prop fitted both with the right spacer kit, though you would need a pretty light boat to spin that prop on a smaller engine.
