Mill Finish is the natural appearance of the aluminum as it comes from the rolling mill (Alcoa, Reynolds, Kaiser, or Alcan) or the extrusion mill. It is as is with no external mechanical or chemical finishing. Extruded metal is considered mill finish. All aluminum has an oxide of some varying thickness. Anodizing is a very heavy controlled oxide.
As they are so small of approximately 5-20 micro-metres in diameter, they do not need valves, as there is a distinct flow from the arterioles supplying the capillary with blood, and the venules draining the capillary within the double circulation.
After oxygen has been moved to the tissue, capillaries join and widen to become small veins and then widen more to become veins, which return blood to the heart. The capillary bed is the network of capillaries supplying an organ. The more metabolically active the cells, the more capillaries it will require to supply nutrients and carry away waste products. Special arteries connect between arterioles and venules and are important in bypassing the flow of blood through the capillaries.