The rigidity of the metal bellows makes the metal bellows or other elastic elements produce a unit displacement required load value is called the stiffness of the element, generally represented by "K". If the elastic properties of the element are non-linear, the stiffness is no longer constant, but changes as the load increases. Nominal stiffness The stiffness given in the design and calculation of the elastic element is called the nominal (or rated) stiffness. It has an error with the measured stiffness of the element, especially the elastic element with nonlinear elastic characteristics. Nominal stiffness represents the stiffness at which point on the curve, it must be carefully considered. Generally speaking, the nominal stiffness is best not to directly use the calculated value of the design, but to use the corrected value of the product prototype after testing. Stiffness tolerance is the allowable dispersion range of stiffness when testing a batch of elastic elements. For the same batch of elastic elements, the rigidity of each element of the stainless steel metal hose is different, and there is a dispersion range. In order to ensure the performance of the components, there must be a limit to the stiffness dispersion range. For elastic sensitive components, the rigidity tolerance requirement is limited to within +/-5% of the nominal value; for general engineering corrugated pipe elastic components, the rigidity tolerance can be limited to within +/-50%.