High-density polyethylene or polypropylene, indicating the color of the insulating wire according to the national standard chromatography; Twist the single insulation into pairs according to different pitches, and use the specified chromatogram combination to identify the wire pairs to reduce the mutual interference and crosstalk between the wires, and the power loss is small.

The common specifications of telephone lines are two-core and four-core, with diameters of 0.4 and 0.5 respectively, and 0.8 and 1.0 in some areas. In addition to two and four cores, there are four, six, eight and ten cores. In general, if the household is in the local mode, 2 cores are enough. If it is used by the company or some group phones, considering the need for broadband use, it is recommended to use 4-core telephone lines. If it is used by digital phones, it is recommended to use 6-core telephone lines.