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.
Arthropods and mollusks have an open circulatory system. In this type of system, there is neither a true heart or capillaries as are found in humans. Instead of a heart, there are blood vessels that act as pumps to force the blood along. Instead of capillaries, blood vessels join directly with open sinuses.