Pedal Assist Sensor for Hollowtech Bottom Bracket type cranksets. This PAS has clips on the magnet disc t oclip to the inside diameter of the smallest chainring on your cranks. In situations where the clips are the wrong spacings you can often get away with allowing it to be held in place by its magnets (depending on chainring metal type). The alternative DIY and most secure route if you only use a single chainring up front, is to drill 8mm holes in the plastic disc and secure to the crank arm using the chainring bolts for your granny ring.
3 Pin Male Julet (Higo compatible) cable type