Where the inner diameter is very thin pipe called "capillary ". Usually refers to the inner diameter is equal to or less than 1 mm of the fine tube, because the diameter of the tube is as thin as hair so called capillary. It can now be seen in medicine, on building materials.
May 2007, the product was inspected at the Air Conditioning Institute of the China Academy of Architectural Sciences (national air conditioning equipment food supervision and inspection center). Take a test example of a node and the results are as follows: