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 should be separated from the large wire laying, weight evenly distributed, when necessary, can be used separate piece separate. High-speed or high-frequency operation, the wires are separated from each other in the level, do not overlay each other in the cable, trachea, tubing, and other more time to recommend the use of the separated piece.