I would say supercharger adapter nut...but then again, when i put mine on, i had to line it up with my other pulleys. Hope you get it
It says "Supercharger adapter Collar (nut)". I think that's the supercharger outlet (or top) collar that connects to the upper IC tube.
Tighten it until its tight. Make sure the pullies line up. Drive it a few days and check to make sure it isn't coming loose.
I have a QH in my garage. Care to do some tuning?
Did it come with a copy of your tune on it?