Place the spring vertically on the flat plate. Without any load, the spring rotates one turn on the wide seat angle ruler to find out the maximum gap between the spring end ring and the angle ruler (check the adjacent second turn from the end to 1 / 2 turn). Measure the clearance with a feeler gauge. After the test, measure the grounding of the other end and both ends of the spring. In the free length, We recommend that the standard Verticality and curvature tolerances (designed to keep non axial forces to a minimum) be 1 ° (in some cases as low as 1 / 2 °).