This patent describes Campagnolo's Portacatena (which roughly translates as 'chain carrier'). It works like this:

• An arc of metal is bolted on the inside of the chain side rear dropout. This arc is roughly the diameter of the top sprocket.
• You then use a gear lever with a special release catch fitted to it, that allows the lever to turn slightly beyond the normal 'top gear' limit of its movement.
• When you release this catch and push the gear lever beyond the normal 'top gear' position, the derailleur shifts the chain over the top cog and onto the arc of metal.
• You can then remove the rear wheel and the chain stays nicely in place, saving on dry-cleaning bills, and allowing the rear wheel to be easily refitted.

So far, so clever, but there was only a small swarm of flies in the ointment. You had to set up the rear derailleur with its top sprocket limiting screw slackened off to allow it to move far enough to shift the chain onto the Portacatena. Then as the gear cable inevitably stretched in normal use there was little to stop you accidentally changing gear into top gear and then onto the, nearly frictionless, Portacatena. This was not exactly perfect when you were just sprinting for that 30 sign. Of course the Campagnolo Nuovo Record and Campagnolo Super Record derailleurs of the time were notorious for being especially imprecise at changing into the top sprocket - so fitting a Portacatena just added the icing to an already rich and flavoursome cake of problems.

• Publisher: UK Intellectual Property Office
• Inventor: Tullio Campagnolo
• Country: UK
• Date: Italian application November 1975, UK application November 1976
• Derailleur brands: Campagnolo
• Derailleurs: none