Shimano made a real effort to add features to justify Shimano 600 turning into Shimano 600 EX. The pulley cage was redesigned to allow you to fit a chain without breaking it (athough, unlike SunTour’s ‘Quick Cage’ , on the one hand you needed a Phillips head screwdriver and on the other the chain was properly ‘trapped’). The pulley cage also had clearance for covering a six speed cassette on Shimano’s new freehub system. The cable clamp bolt became a 6mm allen key bolt, the same as the hanger bolt.
Finally, and most famously (notoriously?), Shimano added psychedelic ‘Arabesque’ patterns. This was just plain weird, but it did make it aesthetically difficult to mix this groupset with others - and it was noticeable how many up-market mass-produced bikes came with complete 600 EX groupsets - a new phenomenon. Probably much appreciated by Timothy Leary and Carlos Castenada.
A fine derailleur - the start of Shimano giving the SunTour V series some serious competition.
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