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.
Arteries do not have valves because the heart provides the pressure needed to send blood through the system. Veins have valves because venous pressure is often not great enoug â¦ h (as the blood must overcome gravity and other forces) to return the blood to the heart. + 103 others found this useful. Natii Carazo.