A digital torque wrench uses a battery operated electronic mechanism that allows users to predetermine and regulate the amount of force applied while tightening bolts or nuts. This type of torque wrench is a more advanced version compared to traditional beam and dial type wrenches. Invented in 1918, the first torque wrench prevented over-tightening of plumbing fixtures. Torque wrenches require recalibration once a year or more depending on the amount of use.
The torque tool usually has an enclosed socket with ratcheting teeth on one end. An adjustment on the socket head allows clockwise or counter clockwise operation. Some models have a pivoting head. Companies manufacture the digital torque wrench in three sizes that accommodate 0.25 inch, 0.375 inch and 0.5 inch (6.35 mm, 9.5 mm, and 12.7 mm) size socket sets. The other end usually has a specially treated handle for gripping. The handle may be machine knurled or covered with a slip resistant material.
Gauging the torque applied on wrenches varies with beam, dial, and digital torque wrenches. The common beam torque wrench generally has a printed scale above the handle and a pointer indicating the amount of applied force. The dial torque wrench requires the user to dial the precise amount of torque needed and then lock the measurement into place. After applying the dialed amount of torque, the socket head slips or clicks. This action prevents the application of further force.
The digital torque wrench has an electronic visual display that alerts the user of the level of applied torque, and some have a mechanized clutch slip or click. On the shaft of the digital torque wrench, lies an electronic mechanism with a liquid crystal display (LCD) or a light emitting diode (LED) display and buttons. The user enters the torque requirements into the wrench using the buttons. Digital tools can display force in foot/pounds, inch/pounds or Newton meter measurements. The wrench displays the increasing increments while tightening.
As the measurement nears the correct amount of torque, the device may beep, buzz, or light up. Some digital wrench models have green, red, and yellow lights that indicate when a wrench applies 80% of the desired torque or reaches the desired tightness. Depending on the digital torque wrench model and price, the tool applies anywhere from zero to 5,000 foot/pounds (6,779 Newton meters) of torque. The digital display also stores torque measurements or allows the user to download them onto a computer for future reference.