The Rover-Landers of BC

Hey guys... so I bought this Lucas TVS alternator to install but am I missing something here? The main post that the blades slide onto has a rail on it. I would assume the rail fits the recess on the blades and so when the post turns so too does the blade. But the blade slides on 'past' the rail so its free spinning. There's a collar coming out of the alternator, behind the blades, but not enough to push the blades forward enough to sit on the rail? So again, am I (literally) missing something? Surely the blades don't free wheel like that. I know its probably a stupid question, and there's probably an easy, obvious answer, but I don't know what it is. Can anyone shed some light?

Does it tighten up correctly with the pulley on? Most modern alternators don't use woodruff keys anymore, as long as the nut is correctly torqued they don't slip.

The pulley clamps the fan tight when tightened on.

Perfect. Thanks for clarifying.

By the way, there are no dumb questions. Always better to ask.