Wilbers Fork Spring - Zero friction - ProgressiveWilbers progressive fork springs friction" Friction reduction through fine grinding, resulting in ZERO friction. In vibratory finishing, the components to be machined, e. g. components, e. g. our fork springs, together with a specially together with a grinding wheel specially adapted for this in a vibrating container, the so called trough vibrator. The vibrations of the container generate a relative movement between the workpiece and the grinding