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 durability and minimizes tooth loss and safety instructions: when using, wear protective goggles and gloves Optimized tooth design penetrates object with ease, cut perfect circles with these tools. Multiscale: 3/4"(19mm),7/8"(22mm),1"(25mm),1-1/4"(32mm),1-1/2"(38mm),1-3/4"(44mm),2"(54mm),2-1/2"(64mm),3"(76mm),3-1/2"(89mm),4"(102mm),5"(127mm)... 12x hole saw sets, 2x mandrels, 1x hex wrench, 1x cushion plate within this plastic case Perfect foe hole:high precision, smooth cutting edges, especially impact resistance, wear resistance, cutting depth 25 mm Suitable for plasterboard, plastic, wood, mdf, aluminum, computer tables etc Read Less