It's the inner PTFE blade tube. By the inner layer of PTFE, the internal surface, the high tensile strength and torque resistance, the high sliding performance (fracture, bending strength) of the blade (torsional strength), kinking resistance, is achieved by the tube. In addition, because you draw the core line in the house, you can control the size of the spindle (internal diameter) with high accuracy. It should be noted that it can accommodate the inside diameter, diameter and blade line spacing, resin, hardness, all of which meet your needs.