I had a saved search on Ebay for the Snap On version and it was probably over a year before any showed up for sale.
I believe Porsche uses the same thread size, so this might be another option...
It should be 5.2 mm. There is a different listing for what appears to be the same part number on Amazon.
http://www.amazon.com/Knipex-7101200-8-Inch-Action-Mini-Bolt/dp/B000SOSC4Y/ref=pd_cp_hi_0