You mean like a slot all the way around the face?
Doesn't mean anything to my knowledge.

 

The balancer has a keyhole slot in it. My crank has no key but looks like you could put a pin on it if you want.
I got this think in the oven right now.
I just wanted to make sure I can put it on without putting a pin in there.

 

Maybe it's for use with a pulley puller for removal.

 

I'm too much of a geek. I saw "ATI" and thought of the video card company.

 

I got it on there. I was told it was for blower or extreme RPM engines where a pin is needed.

 

Ah ok, that makes sense.
I've never seen a ATI pulley (mine was a ASP) so it was hard for me to picture hehe.