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.
Whereas a blood capillary has an arterial and a venous end, a lymph capillary has no arterial end. Instead, each lymph capillary originates as a closed tube. Lymph capillaries also have a larger and more irregular lumen (inner space) than blood capillaries and are more permeable.