The new SiSL2 Hollowgram road 109mm spindle. Cannondale has redesigned this spindle to work optimally with the new Hollowgram design.
It is lighter and looks a little different than the previous road spindle. You will notice there is no shoulder on this spindle and you will need to look at the end and it is written which is the drive side.
As shown in the diagram a complete bottom bracket for the SiSL2 crankset requires specific drive and non drive side spacers.