Craig, I will send you six sets from the next batch.
Paul, We still cling to our old systems of measurements over here. Paul got it right, they are about 4.2 mm in diameter. The heads on these ones are 11.2 mm. The 1/2" and 9/16" ones translate to 12.7 mm and 14.3 mm, respectively. If you need to match a specific diameter for the bolt and nut heads, I can do that. Matching a specific thread may or may not be possible.
Ian, Thanks for doing the math for me. Some days I think metric would be a welcome change...