Screwdriver bits are made from S2 stainless tool steel, more durable than CR-V steel. They achieve an HRC (60-65) hardness and are not easy to bend and break. Tool Set The tool set contains the recessed bits. Even if the screw is deep and narrow, it can be easily removed. It also contains special screwdrivers for rusted and broken screws, suitable for low speed electric drills. Complete Set This precision mechanical screwdriver set contains 115 precision bits and 20 necessary disassembly accessories. Each drill is unique and the type is different. With the Magnetic Screw Mat, the screws can be collected more cleanly, thus effectively avoiding losses. Multifunctional Application The 135 in 1 Precision Mechanical Screwdriver Set can be used to repair electronic devices such as cell phones, laptops, cameras and household appliances such as televisions, air conditioners, refrigerators, cars, etc. It is a set of repair tools ideal for disassembling and maintaining glasses and watches.