Chuck Schmidt <chuckschmidt@earthlink.net> writes: There is this note in the Campagnolo Timeline at http://www.velo-retro.com "1961 - In July a revised Gran Sport rear derailleur is introduced with a 10mm spring cover (was 8mm) to improve shifting on six-speed freewheels. Note that six-speed freewheels are not commonplace until the mid-1970s!"
but they <were> ubiquitous.
e-RICHIE
chester, ct