So what's the deal with woodruff keys?

[Andy]

Maybe it's also separate because then, a builder can replace the keys. I've actually never known any to do that, but maybe in older cars, it would be a good idea. Also, I'd imagine they could be made stronger and like RJ said, cheaper, than if it had to be machined from the crank or cast with it. But in keeping with your initial insights, I actually saw a Miata with the crank snout snapped out. Amazingly, the crank pulley was still sitting inside the engine bay, and not thrown out like a bullet.