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: 27, 44 mm.