I have been sewing for many, many years and put miles and miles of sewing on my machines. You can feel of the needles and use your finger nails to feel for burrs. If so either throw it away or file it if possible. I usually just threw them away as I had already gotten my moneys worth. Also learn to feel the tip. Use a new needle and compare it to the used one. You will soon be doing this as a regular check just like taking care of your machine. Hope this helps. I still have a lot of needles, but am too chinzy to waste them.