looks like that's a fan blade
Comparing these details (taken from the big twitter images that tricityb linked in post #175) with the picture of posted by Stumpy Grinder in #185 that shows a worker assembling the fan, I can identify the curved line separating the two types of surface on the blade and the rounded ridge that locks the blade to the hub.
Last edited by Musician; 4th Oct 2017 at 10:12.
Reason: gamma enhanced detail uploaded