Removing rear brake rotors on an A4

[DocWyte]

Well, I had everything disassembled on my friends
'99.5 A4 and was ready to remove the rear rotor.
Looking at the replacement rotor it looked like there
was no set screw and the rotor simply sat on the hub.

Looking at his stock rear rotor there is a large nut
in the center of it, that's an allen head.  A large
allen head, at least a 13+mm one.  I'm assuming this
has to come off to remove the rear rotor.  Two
questions...

What size is that allen head?
What the heck do I do with it once I've gotten it off?
 It can't be used with the replacement rotor...

TIA!

-josh

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Josh Wyte
Momentum Motorsports
508-833-3024 After 5 pm EST

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