The mm part they are talking is referring to the tie rod size thickness
For the 2006 Model Year GM did a 14mm tie rod size
For 2007-2010 GM updated the size to 16mm
That being said, both 14MM and 16mm will work on any model year. THAT BEING SAID, you have to have both the INNER and OUTER tie rods be both the SAME SIZE because tie rods are made up of 2 PIECES.
Personally, I would recommend upgrading to the 16MM because they are a little stronger and less likely to snap when offroad. If you never go offroad or never intend to go offroad, 14mm will work just fine if they are the only thing you can get.
If you haven't ordered them already, I would buy TIMKEN for the wheel hub bearings. They are basically OEM quality and TIMKEN actually makes a lot of OE GM Genuine Parts for GM. They cost less than then GM Genuine and are the same thing.
For ball joints and tie rod ends I would go with GM Genuine. Please do not go on eBay and buy Detroit Axle crap. The quality is nowhere near as good. I would recommend purchasing parts from RockAuto.
