TAC-41 cylinder head “GBB” Optional cylinder head for the TAC-41, “GBB” version, for optional/GBB hopup unit (SBA-HOP-31). 4.60 internal diameter nozzle, Oring included, stainless steel CNC construction.   Compatible with (must be used with a “GBB” hopup unit- SBA-HOP-31):   – original TAC-41 piston (SBA-BPS-30) – variable mass piston for TAC-41 (SBA-BPS-31) – Advanced piston head “GBB” (SBA-BPH-02) NOT COMPATIBLE WITH SBA-BPS-15 AND SBA-BPH-01