The Shimano Dura-Ace Di2 SW-7971 Bar End Shifter is made from engineering grade plastic with two buttons on each stub end. It attaches to the ends of your aerobars via an expander bolt that is identical to expander bolts on mechanical Shimano Dura-Ace bar end shifters. Put 'em in, use an Allen key to expand the bolts, run the wires, and go. As good as it is for time-trialing, we see a great opportunities for roadies who hate having a separate time trial rig. Here, you can have your normal Di2 levers AND have your time trial setup. Just bolt on the bars, plug in the wires, and go.
While they do come set as a "right" or "left" shifter at the factory, there really is no fixed right or left shifter. Just as with the electronic dual control time trial levers, you can run these so the buttons are on the inside or the outside, you can also set which button is the upshift and which is the downshift, provided you have Shimano's Di2 diagnostic tool, SM-EC79. As with the electronic dual control time trial levers, these have a fairly light touch, feeling a bit like mouse clicks. Each press of each button is shifting up or down one cog or chain ring.
These switches must be run with either Shimano's Dura-Ace Di2 Dual Control road or Dual Control time trial levers. They cannot be run on their own, nor can they be used with Ultegra Di2.
