04-04-15, 04:36 PM
Just a thought & I maybe wrong, but if the stud you are drilling out is 6mm would it not be better to tap a 8mm thread into the head,so purchase a 8mm to 6mm exhaust stud of the required length & correct thread pitch.
http://www.ebay.co.uk/itm/Motorcycle-exh...1e6b04cdfc
http://www.ebay.co.uk/itm/Motorcycle-exh...1e6b04cdfc