Maybe a needle in a haystack kind of question. But does anybody know what this rear derailleur hanger fits? It's been in the parts box for a couple years. I mostly work on vintage-ish road bike stuff so likely along those lines. Thank you.

Looks like this one, which they say was used by "Airborne, Avanti, Bergamont, Breezer, Brisa, Centurion, Cinelli, Coluer, Corratec, Cube, DaBomb, Diamondback, Focus, Fuji, Go Sport, GT Bicycles, Hasa, Intec, Kalkhoff, KHS, KTM, Marin, Massi, Mongoose, Nakamura, Nirve, Orbea, Qbike, Raleigh, Saracen, Schwinn, Scrapper, Vario, Venzo, Viper, Wheeler, ..." (3 dots meaning more as well?)

I know practically nothing about this "dropouts.info" website other than they seem to sell lots of different style hangers, appears to be hundreds of them. Oh I see they say "1000+". In German, with prices listed in Euro. But of course you're not interested in buying one, this is just an informational database.

https://wheelsmfg.com/derailleur-han...r-hangers.html

Ah yes it looks like #9:
https://wheelsmfg.com/derailleur-han...-hanger-9.html

They say it's for GT, KHS and Marin

That sure does look like it. Thank you.