Hollowgram 137mm Bottom bracket. This bottom bracket is not specific to the SiSL2 Arms, any Si or SiSL will work. This system utilizes a dual configuration of spacers and a wave washer on the non-drive side. Includes FSA bearings, all necessary spacers for your application and 12 point engagement bolts - along with a set of the new SL2 bearing shields to match. Available in both Si and Ai spacing variants.
Not sure what BB you need?
Si: Bottom Bracket has an offset (dish) which brings it in towards the frameset. This is the most common configuration, and is used on all Scalpels up to 2016, F29 Hardtails, Jekyll, Trigger and Habit.
Ai: Bottom Bracket has very little offset (dish) which appears flat. This is the new system on the F-Si and 2017 Scalpel Si.