my great grandpa has this strange old fasioned thing that i think was used as gear for scuba diving about 100 years or so ago. do you have any idea what this may be
here is a video
just copy and paste the link

I don’t recognise it at all.

Are you sure it’s actually a piece of scuba gear, and not something your great-grandad recovered from a shipwreck, such as a cover for a ship’s compass, or a running light?

You might have better luck posting this question on a dedicated scuba board, especially one devoted to vintage gear and/or shipwrecks. You can find such boards at e.g.