Jack, if you have any of the parts manuals, you can decode most bolt/nut sizes from the part number.
Lookup the riser's nuts. If the number has something like 010xx, it's a 10mm, 008xx would be 8mm.
Forum search 'decoding part numbers' should have more info.
Edit: Waitaminit, the riser posts are shouldered. Failing memory sez 10mm posts with 8mm threads.
Best wait for confirmation on this...