The selection principle of towline 
 High within: select the most coarse of a built-in cable, tubing, trachea, plumbing as a reference height, plus at least 10% of the height of space as the towline within the high the Hi if overlapping according to overlap the actual height as the reference height . 
 Inside Width: Choose coarse cables, tubing, trachea, water pipe, its diameter, and the towline within wide reference and left at least 10% of the width of the space. 
 Bending radius: built-in cable, tubing, trachea, plumbing, and the largest bending radius as a reference value, and left more than 10 percent of the space, the towline built-in cable, tubing, pipes, and tracheal placement guidelines. 
 15% of the remaining space should be left, so that the built-in cable, tubing and other free activities do not generate tension in the radius direction of the towline. 
 The diameter difference between the big wires should be separated from laying, the weight is evenly distributed, if necessary, available separate piece separate.