Where did this screw come from?

[No longer active on TMGA]

The last time I flew, I found this screw (see picture) rolling around on the top of the glare shield, just ahead of the compass. It's a round head, countersunk, non-magnetic metric screw with a 4 mm thread and a 10 mm threaded portion. I'm not aware of that size being used anywhere in the Phoenix, I don't see any empty holes where it might have come from, and I have hard time imagining how it got onto the top of the glare shield and stayed there.

I haven't had any negative G loading before the found the screw, so it seems unlikely it bounced out of the canopy ducting or somewhere else.

Any ideas?

[Jim Lee]

That looks like the screw from the back side of the whiskey compass.

[No longer active on TMGA]

That was it! I looked today, and this time I could see the screw was missing. It was hard to see the screw wasn't there, given the poor hangar lighting; also, I assumed the compass had SAE screws for no good reason.