Cargo bay
From Kerbal Space Program Wiki
A cargo bay is a part which can contain other equipment. The main usage is to store unwieldy or unstackable parts (such as a small probe) within a larger structure. It also shields the parts from aerodynamic drag.[citation needed]
Currently the game has 2 cargo bays, the Mk2 Cargo Bay CRG-04 and the Mk2 Cargo Bay CRG-08. They are both Mk2 sized.