Needle files don’t work very well when they are dirty and caked with debris. To clean them, use a small clean jar of choice. I like to use pickle jars, but if you prefer olives go right ahead. Fill it with lacquer thinner. Put the the clogged needle files into the thinner, making sure not to submerge the rubber ends of the files. Close the lid to avoid fumes, and then wait for about an hour or so. Remove the file, and clean it off with a stiff brush. An extra tooth brush will do. Then you’ll be good to go with your next modelling project.