Extension springs (also called extension springs, or extension springs for short) is a spiral spring that bears axial tension. When not under load, the extension springs between the ring and ring are generally not tight clearance.
The initial tension of a extension springs: The initial tension is equal to the force required to pull the spring into contact with each other. The initial tension occurs after the spring is rolled. Torsion spring, because of wire material, wire diameter, spring index, electrostatic, lubricating oil, heat treatment, electroplating, make each tensile spring initial produce uneven phenomenon. Therefore, when installing the extension springss of various specifications, they should be pulled in advance to slightly separate the parallel rings. The force required becomes the initial tension.