It was a typo and the 10mm and 12mm in the instructions should have been referred to as M10 and M12 bolts; the socket sizes are correct for installation of the Curt Trailer Hitch Receiver # 13364 or etrailer Trailer Hitch Receiver # e98854 on your 2009 Volkswagen Routan.
You can see this in the linked installation video I added of this hitch being put on an '09 Routan. view full answer...