Thanks for the response. The headlight didn't fall out, just the clip that was attached to the top screw. There is no back to the headlamp assembly (casquette?), so the clip fell out and onto the ground.
To my knowledge, the clip wasn't holding anything. When I replaced bulbs with LEDs, I saw it hanging there and wondered what it's purpose was. I tried to connect it to -anything- with no success. Granted, that's while the headlight was out, so if it was supposed to be tightened to a rim, that didn't happen (and it wasn't holding anything on). After reading your response again, perhaps it doesn't do anything with the stock light?
If I recall correctly, on my bike (AVL) the outer headlight ring has a lip on top that rests on a small ridge (holding it in place). The bottom of the ring has a hole and is attached by a small screw (which can be a bit of a bear to get back in). There are two other small screws on the outside that hold on the inner rim. There are three screws on the inner rim that can be loosened and it then turns and can be pulled off, freeing the headlight.
The front of the outside rim has two open holes. I'm not sure what their purpose is.
Rob
If something fell off inside the headlight, it should still be there. Did the headlight fall out? Since my whole headlight fell out and the clip had unscrewed and fill out with the headlight. I tried to find another one and ended up getting one from a vintage Triumph parts store. But it's real purpose isn't adjustment, although that is the secondary use of the slot, it's really used to keep the headlight in if you get the optional ones that have a separate trim ring ahead of the one that is one piece on the stock version.