Belt Tensioner Pulley Nut Size?

I am trying to change my belt tensioner pulley assembly and can't find out the size of the nut to do so.

It's the Dayco part # 89367

http://www.rockauto.com/catalog/moreinfo.php?pk=1115458

Or Gates part # 38365

http://www.rockauto.com/catalog/moreinfo.php?pk=1058048

Or the Goodyear part # 49365

http://www.rockauto.com/catalog/moreinfo.php?pk=1334685

It looks like a 6 point star head? Is that accurate?

Does anyone have a diagram on how to change it if so?

Thanks!