I was once flying my aircraft, a Robin DR400/100, on a nice little day trip. Shortly after the initial climb out just levelled off and set up in the cruise, I noticed a 60mm long M6 Allen head bolt and penny washer rolling about in the passenger side foot well. As you can imagine this grabbed my attention. A quick check that all the controls worked normally then a gentle rate one turn for home. It took me and the licenced engineer a couple of days to find its origin. It turned out to be one of the bolts that secure the instrument panel to the airframe.
All this has shades of Le Mans 66 Ford Vs Ferrari, when Matt Damon, AKA Carroll Shelby, walks over to the front of Ferrari pit and quietly drops a nut on the deck soon after one of the Ferrari`s has not long left the pit following service, creating confusion when one of the service crew spots it.... ? (-:
Sorry for the thread drift Andy, it`s a bit of a TM thing....Nice pic of the screws, Thanks for posting Paul, I wish I knew where they might have come from...