Hmmm... Mr. PET is telling me that they're M5x18, but that doesn't sound right. I'm thinking M6x20mm or M6x25mm, with the standard thread pitch. What is that, 1.0 I think?
Hopefully I can order more of those stupid nuts, now that I've found them with the help of Mr. PET. I had tried looking through my hard-copy book long ago and couldn't come up with the correct part number--looks like I finally found it!
--DD