Bead on Bottom of Disc

What is the bead on the bottom of the disc for. 

I looked at several discs and the one difference is the bead on the bottom. A R-Pro Aviar v. R-Pro Aviar X. People have talked about it with a Nuke or a Nuke+ and a few other discs. 

What is the bead for or how does it help or hinder a disc? 

[Ryan Rios]

It adds stability. Think about how a buzzz is a wasp without the bead.
All the cool ones have it ;)

[eddie martinez]

scrape it off and see what happens