Official Answer
Answer
A wave spring's outside diameter $O.D.$ increases during compression. The theoretical expansion $\Delta D$ can be estimated by $\Delta D = \sqrt{D_m^2 + \frac{(L_f^2 - L_w^2)}{N^2}} - D_m$ where $L_f$ is the developed length of one wave and $L_w$ is the projected length. A rule of thumb is to provide a diametrical clearance of at least $0.05$ mm per $10$ mm of diameter. If the spring contacts the bore wall, friction will cause a significant increase in the apparent spring rate and potential galling of the housing.
