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.
Red blood cells squeeze through capillaries single file. Unlike arteries and veins, capillaries do not have specific names, but are named collectively for the region that they supply. Capillaries in the lungs, for example, are called pulmonary capillaries, and those in the stomach are the gastric capillaries.