What are the considerations for calculating the spring rate of a single-turn wave spring with overlapping ends?

The overlap or 'Lap' type wave spring provides a nearly continuous circular contact surface. The spring rate calculation must include a correction factor for the overlap region which acts as a stiffener. The formula $P = \frac{4 E b t^3 N^4 f}{I D_m^3}$ is modified where $I$ is an empirical factor typically ranging from $1.1$ to $1.4$ depending on the overlap arc length. If the overlap is too large, the spring will behave unevenly; if too small, the ends may clash under load. For medical devices, this overlap ensures no gap is present that could trap debris or cause localized stress concentrations on the mating assembly.