Satellite Drops Sprint Shifter (12 speed)
The new SW-RS801-S sprint shifter was introduced when Shimano released Ultegra R8100 / R9200 to the world. It enables fast shifting from the drops of 12-speed Di2 bikes.
These connect to the special Satellite Shifter port only found on the 12-speed shift levers. This is always the bottom port. They will not work in any regular SD300 port.
While previous satellite shifters were one unit, these newer ones consist of a shifting unit and a clamp, or band. In theory, you could actually stick the unit onto your handlebar using some strong double-sided tape,
Alternatively, slide the unit onto the band and then use the provided double-sided tape to attach it to the handlebar. You then wrap the bar tape over it to secure the shifter.
These are sold as a pair, weigh 3.1g each, and come with a 100mm wire.
Note that while these are part of the DURA-ACE R9200 series, they will work on the 12 speed Ultegra R8100 too, of course.
105 Shifters do not have extension ports, and these satellite shifters cannot be used with 105 shift levers.