Take the iron casing insect nylon tube as outside protecting housing's seven-core electric cable coil Cheng Xian is the good way which the main engine and the semitrailer, the trailer tractor, the trailer electric circuit connects, the coil has the endophragm to be smooth, the compressed air or pneumatic brake responds quickly, the loss of pressure few, wear-resisting, bears characteristics and so on aging, good elasticity, widely uses in each kind of trailer tractor, the semitrailer, the trailer and each kind of braking system's connection pipeline.