A torque screwdriver is a tool used to turn the screw head fasteners to a precise and even tension. Torque is a measure of turning strength used to twist an object. The English system measures torque in units of feet pounds or inches pounds, and the metric system uses Newton meters. Manually operated, pneumatic, and electric versions of torque screwdriver are available to meet the needs of almost any size project. Most torque screwdrivers are adjustable within a range of torque strengths to accommodate multiple applications.
Manual torque screwdrivers generally have an in-line drive shaft and handle similar to the traditional screwdrivers. Electric models can have the same form or have an offset handle that makes them look more like an electric drill. A pneumatic or air driven torque wrench almost always looks like a drill and is usually the most powerful range of torque screwdriver.
The unique operational feature of a torque screwdriver is the pressure sensitive clutch. This built-in limiter controls the maximum torque used on the screw by connecting the drive connection to a preset torque level. Adjusting the clutch position allows the user to set torque within the range offered by the tool. Most manual and air driven torque screwdrivers have slip-clutch and cam-over designs that allow the tool to continue operation as the drive gears separate. Automatic shutdown clutches go a step further by turning off the electronic torque screwdriver completely to allow even more precise control torque.
Corporate manufacturing operations often use torque screwdrivers to attach multiple links to a product with equal pressure. Torque screwdrivers greatly reduce variations between screw lock attachments that are common when multiple builders are completing a large project together. Equally driven screws increase the structural integrity and overall stability of a composite object. Overdriving a screw often divides the material or damages the threads and eventually weakens the fasteners’ connection. Sending the screw in too short cannot drive it into the other surface and make the connection.
Torque screwdrivers that get regular use are often tested and recalibrated to ensure a constant torque. A machine called a torque tester is attached to the head of the tool to provide a reading of the applied torque when the torque screwdriver is fully engaged. Damage from extensive use can cause bends and cracks in the gears of a torque screwdriver that allows it to maintain a set torque value.