This design allows shooter to use SureFire XC-1 in conjunction with an AR front sight.
ROSCH Works was the first to being this design with SLM1, and now there is one for XC-1
Price: $95
Link:
https://tangodown.com/shop/tangodowntm-light-portal-front-sight-ffa-02/
From: TangoDown vis Soldier Systems Daily