The choice mostly depends on your application. The flat bar and rod are some of the standard aluminum alloy shapes, but their applications may differ. While both are linear, they have different cross-sectional geometry. For both, the elongated status suits applications where easy machining is necessary. The products are also strong along their length, so the applications should suit such properties. You will mostly use the rods in shafts in machinery. The 7075 aluminum flat bar is preferred in marine, automotive, and aerospace applications.