Neither metallic nor various polymer plain bearings performed ideally in tests of "Erwin Koppe - Keramische Heizgeräte GmbH". Metallic ball bearings not only seized too fast, but were too loud in operation. Alternative tests with polymer plain bearings led to excessive coefficients of friction, so that these were also discarded. The problem was to find a component that keeps the complete mechanism running despite very small installation space and is also durable, temperature-resistant and insensitive to dirt.