At the end of the 1950s Campagnolo's patents on the parallelogram derailleur had run out, and a slew of more affordable competitors emerged from Simplex, Huret, Gian Robert, the Cyclo Gear Company, Old Uncle Tom Cobbley and all. Campagnolo's response was to spend the early 1960s producing a, slightly random, sequence of 'inexpensive' derailleurs designed to sit below the Campagnolo Gran Sport.
This beguiling derailleur was one of this sequence. It has (uniquely for the time) no obvious model name and only 'Campagnolo' cast into the outer parallelogram plate. It seems extraordinarily similar to an early 1960s Campagnolo Gran Sport, but with, lower cost, Cadmium plating on the parallelogram and, even lower cost, black oxide finish on the pulley cage plates (which, unlike the Campagnolo Turismo are cast not pressed). There is also no writing on the inner parallelogram plate. Offering it alongside Campagnolo Gran Sport is a strange decision - a bit like the Rolling Stones choosing to go on tour with a Rolling Stones tribute band as support act.