How to use: Insert the catheter into one end of the thread and feel the clockwise rotation of the tool when you touch the filter. At this time, the threaded part will catch the filter. (The end of the filter has a closed end, this design is for you to extract it, If your filter is reversed, it will break into the filter when it is extracted.) When you jam the filter, you will feel resistance to rotation. At this time, you can pull it out.