Size of the Fantastic Fan Screw

A few weeks ago we went from Florida to Kansas and back using only backroads -- it was really fun and really bumpy. As to the bumpy part, at one point I got into the t@b and noticed the hand crank to raise and lower the exterior fantastic fan cover on the floor.  Apparently the screw holding it in place worked itself loose and fell out.  Once we got home I emptied everything out and searched, but I never found that screw.  There were places that it could have rolled under that are just impossible for me to access without serious disassembly.  

The crank still works, but it doesn't stay in place.   Can anyone tell me the size of the screw so that I can get a replacement?

Any help would be greatly appreciated.