These are Gauge Blocks, precision ground pieces of steel so flat and smooth that they stick together, the phenomenon behind the wringing is still unknown! https://t.co/HLX77XkAI0 https://video.twimg.com/amplify_video/1774397642161655809/vid/avc1/480x852/M41L7ad8qT_oFps7.mp4?tag=14