I've always wondered the same thing for peanuts. Is a peanut the small nut with the papery cover or is a peanut the single/double/triple nut with the cardboardy cover?
For walnuts, I think the double item that comes inside a single shell is ONE walnut. If you are very careful, you can remove it all as one single piece - so it must be one.
However, 14 halves is listed as one ounce in the USDA Nutrient Database, so I suspect that is one SB serving.
And pecans are structured very similarly.
Started 9th of April 2007; Started IP protocol 20th September, 2012 at 193 pounds.
Reached goal March 2013; Maintained via Paleo/Primal since.