On my previous S8 I used stainless steel ones from RS components.
Next time round I'm going to use aluminium ones from ebay, easier to tap threads deeper and file down if needed.
http://forum.a8parts.co.uk/showpost....5&postcount=12
http://www.ebay.co.uk/itm/L800-M8-8m...item3cc0090445
and for the other end use a male track rod end, then you actually wont need to do any tapping of the female one, just cut/file down the male one if its too long.
http://www.ebay.co.uk/itm/Track-Rod-...item4ad8cb72f4
and yes, its nothing to do with secondary air injection
