I'm not sure this is the best I've got, but it's unusual anyway.
Trivelox Model B derailleur, introduced in 1937.
I had never heard of Trivelox until I read about it on BF. This website is always educational! Do you have the full Trivelox setup, with the sliding cog hub?
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069