The FK 9 wave spring is primarily used for tensioning and readjusting in high-temperature applications. This makes them suitable, for example, for use in exhaust plug-in connections. Here, an FK 5-HFL Fey laminar ring can be tensioned to cover the sealing gap of the plug-in connection. The resulting double sealing line can reduce leakage.

Axial movements due to thermal expansion are offset by the spring movement. Use of this sealing technology is limited to static applications.