This Z=0 switch uses a lever mounted on a HDD bearing to allow very fine control of the Z=0 position in a 3D printer. The lever effectively multiplies the adjuster screw TPI by about 8, making a 32 TPI screw look like a 250 TPI screw. One full turn of the screw will move the print bed about 100 um. There is a small magnet on the end of the lever to keep the lever in contact with the adjuster screw. Video of the operation here: https://vimeo.com/208080500