Please tell me what this is.

Tonight while shooting my lens and or camera shutter was sticking. I realized it was the gaff i put on the switches that may have been preventing the Lens to seat properly. But then on the seat I have my gear in i see this rubber ring. Please tell me it did not fall off a lens or the camera?!

I can't tell from just that one picture, but what lens(es) were you using? Looks like it could be a weather sealing gasket from a lens possibly, it doesn't look like it's likely part of the camera.

I googled it. It is the rubber ring on the back of the 17-55.

Where are you putting gaff tape?

And why?

Looks like an O-ring seal for a STS solid rocket booster to me. Where exactly were you on 1/28/86?

I have gaff on the switches. I cover all my switches with gaff because I have a bad habit of switching the AF or OS/IS off when shooting or swapping lenses. And it was not the gaff after all, it was the rubber ring that fell off.