I had written to Kymco about that--they said 8mm but did not sound entirely sure. I've copied their e-mail below--just doesn't seem as certain as they should be. I would measure first. As I am also thinking about getting these, I'm hoping to check this weekend. I am also planning to write to the seller to find out about the threading issue. Per wkrebs helpful videos (find his stuff on the super 8 150 forum) both mirrors have to be unscrewed in a counterclockwise direction. I don't know if that is what they refer to as standard threading, though.
From: Drazan Jerkovic [mailto:djerkovic@kymcousa.com]
Sent: Wednesday, May 14, 2014 2:59 PM
To: 'Getinfo'
Subject: RE: mirrors
It should be 8mm
Drazan Jerkovic
Warehouse Manager
Kymco USA
www.kymcousa.com