The Ultegra Di2 ST6871 11-speed brake/shift levers attach to a TT/Tri base bar (aka as a bullhorn) to provide braking and perhaps more importantly an alternate location to make shifts. More locations to shift from means you can always be in the most efficient gear and there is no struggling to get back on the aero bars to make a shift. This can save lost time and also increase safety because the times you are on the bullhorns are generally for turns, climbs, bad pavement and crosswinds -- when shifting from an aero bar may to be the safest idea. These are similar to the Dura-Ace 9071 TT levers but have an alloy brake lever instead of carbon.

ST-6871 TT/Tri reverse levers have built-in E-tube wires with no additional E-tube ports. They required an inner bar diameter of 19.0 - 22.5mm and an outer diameter of 22.2 - 24.0mm.

The Ultegra Di2 STI levers are one part of the Di2 system including shifters, derailleurs, battery, battery charger, and etube cables/wires.