Hole Saw Drill Bit set (16 pcs)Safety and durable: heat treated hss,the special gear design makes the hole more accurate. high speed steel teeth for fast and clean cuts. suitable for normal wood,don't try it to hard material. it will happen broken. all pieces in the set are heat treated enabling them to be suitable for soft and hard wood, plasterboard, plastic,aluminum and non ferrous metals Sharper teeth for faster cutting and easy plug; increased wall thickness improves