Thanks all for helping out with this. Here’s some FYI’s to fill in the gaps. We found that the original 3/8″ Truss Rod nut was not close enough to 10mm to satisfy our European customers, whereas 5/16″ and 8mm was a perfect match! This was a nice contribution to world peace so it became the standard about 2011. If you’d like to be sure regarding your personal guitar; go to http://www.santacruzguitar.com/careandfeeding and using your serial and model number as reference you’ll see what size nut is on your truss rod.
The thin walled socket is only recommended to keep it from binding between the old 3/8″ nut and the wall of the access hole. With today’s 5/16″ nut there is ample clearance with no chance of binding, making any standard issue socket appropriate for the task.