This is the External Tank (ET) and Solid Rocket Booster (SRB) forward attach point. The dome houses the honeycomb that absorbs the impact of the frangible nut. The green primer is on metal that belongs to the ET. The bottom structure with the red stripe is SRB. The ET sits on top of the SRB; hence, the SRBs lift the vehicle off the pad during launch. The forward attach points carry the entire thrust load during launch.