74 xs650 advance spring question

[650Skull]

'Moon key'? Never heard it called that before, but shouldn't that be 'half moon key'. Personally, I call them them 'Woodruff keys'!
I better add this to help you out - LOL...

That aside, there's probably no half moon key in there, half the time the rotor pushes them out as it's installed.

I bash the keys a little to make them a tight fit.

FYI. For what ever reason, HHB has never sold or advercated his PMA systems b used with a moon/woodruff key.