Answer
A 'Pilot Diameter' is the shaft diameter that centers the wave spring. The tolerance on this pilot is critical for preventing axial misalignment. For a wave spring with a nominal ID, the shaft pilot should be $D_{pilot} = ID_{min} - 0.010$ inches. The tolerance on the pilot should be held to $\pm 0.002$ inches. If the pilot is too large, the spring will bind as it expands/contracts; if too small, the spring can sit eccentrically, causing 'edge loading.' Edge loading increases the local stress by a factor of $K_e \approx 1.5$ to $2.0$, which can lead to fatigue failure within $10^4$ cycles. In high-vibration automotive transmissions, a precise pilot fit ensures the spring remains concentric, maintaining a consistent preload on the bearing race it supports.
