What's this?

[Space-Kook]

Rummaging around with a magnet trying to find a bolt I dropped and fished up this instead. Was below the flywheel area resting on the chassis.
What is it? (Bonnet pin for scale).

[malcolm]

No idea but maybe homemade, looks a bit uneven at the top,could be an anchor or tab for a spring but can't see a small hole for spring to hook thru.

[jkhackney]

Maybe it was a keychain attached to a spare key hidden on the crossmember?

Or a dog tag? I found one in my Series 1 (but it was alu, not magnetic).

[Herald1360]

Looks like a SU carb tag. Does it have any numbers embossed on it?

[Space-Kook]

No numbers or marks on either side unfortunately.

Appreciate everyone's input, thanks all.