@Nav, I couldn’t find a good photo of the Fly so I drew one for you. It’s a shot in the dark, but if you have a magnet slowly work it over the area where you removed the tumbler from the hammer. The Fly is tiny, so be methodical on your work bench and floor. If you find it put it in a closed container for safe keeping! When you remove the tumbler you’ll easily see the groove where it fits and the hole that the stem on the Fly fits into. Make sure it’s clean and lightly oiled.