This nut was hand-engraved with "KK," "9", "W", and "W." It resembles the a DMM Wallnut but has greater curvature. DMM confirmed that it is not a DMM Wallnut or DMM prototype. The "KK" mark prompted me to ask Kris Kirk. He confirmed that it was not a CMI nut. We are still trying to identify this nut.

↑ 178: KK; #9

• Made in [ca. 1990].
• Size: 27x44 mm.
• Anodized aluminum alloy.
• Manually labeled with "KK," "9,", "W," and "W" in corners of top surface.
• This one is a mystery! I purchased it from a U.K. seller who could not identify it.
  DMM confirmed that it is not a DMM Wallnut or prototype of theirs.
  Kris Kirk at CMI confirmed that it is nothing that CMI has ever seen.