The Campagnolo 12s UL Chain Pin is needed whenever you repair, lengthen or shorten a Campagnolo 12-speed chain.
The Campagnolo 12-Speed drivetrain requires the use of Campagnolo's 12-speed chain. The only way to join the ends of the 12 speed 5.15mm chain, either new out of the box or when re-sizing, is by using this Campagnolo UltraLink CN-SR600 pin. Visually distinct from the two-color 11-speed pin, the CN-SR600 12 speed pin is shiny all over and can only be used with 12-speed chains.
As with the chain, Campagnolo also requires use of their UT-CN300 Chain Tool (sold separately), which is not only used to break chains properly but also to drive and peen the pin precisely. This exacting process becomes even more crucial with flush pin design of the 5.15mm chain. The UT-CN300 Chain Tool has a specially designed, ultra precise, tapered tip end the driving pin on the tool. The Campagnolo 12-Speed chain will come with highly specific instructions that are also available on the Campagnolo website. If you do not have the correct tool and informed experience, take your bike and chain/pin to your nearest Campagnolo Service Center or trusted mechanic for installation.