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A torque screwdriver is a screwdriver with components that ensure tightening to a specified torque, ensuring tightening which is sufficient, but not excessive. An insufficiently tightened screw connection may loosen in operation, and excessive tightening can damage parts; for example, if the nuts holding the wheel of a car in place are too loose, or damaged by overtightening, a wheel may come off at speed. Torque screwdrivers are used in mechanical production, manufacturing, and maintenance; their use is part of quality assurance. Most torque screwdrivers allow the torque to be set to any value within a range. All have a torque-limiting clutch that disengages once the preset torque has been reached. Torque screwdrivers can exert torques from 6 inch ounces (0.04Nm) to at least 27Nm,〔 although no single tool covers the entire range; low-, mid-, and high-torque ranges are available. Torque screwdrivers and torque wrenches have similar purposes and mechanisms. ==Torque-limiting clutch== The clutch is the component that defines a torque screwdriver. This is achieved with steel balls rolling between indented plates, compressed by a spring at one end, and the other side driving a screw or fastener. The torque limiting clutch is the part of the tool that limits the amount of torque being applied to the fastener at the receiving end of the tool. On simpler tools the clutch settings may be marked with arbitrary numbers (e.g., from 1 for the lowest available torque to 20 for the highest, without necessarily having a linear relationship with actual torque) rather than torque values. Torque screwdrivers are available with several types of clutch, including “cam-over”, “cushion clutch”, and “auto shutoff”. Most of these clutch types are used in electric screwdrivers, air screwdrivers, impulse screwdrivers, manual torque screwdrivers, and cordless torque screwdrivers. Each type has the ability to preset a specified torque value. In some cases a tool may need to be certified in a calibration lab to verify its torque output; a certificate may be issued by an organisation such as NIST in the USA. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Torque screwdriver」の詳細全文を読む スポンサード リンク
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