Torque wrenches are used to precisely apply a certain amount of torque (twisting pressure) to fasteners such as nuts, bolts and screws. They consist of two basic components--a socket wrench type mechanism and an internal torque reading mechanism. There are three major types of torque wrenches to choose from: the beam type (measures the specific amount of bend in an elastic metal arm); the click type (utilizes a calibrated clutch to allow slippage when a certain level of torque is attained); the electronic type (utilizes an electronic strain gauge) to measure torque being applied. Choosing a torque wrench is easy to do by following a five-step process.
Determine what the average or usual torque setting will be when you use your torque wrench. Will you be torquing large components on a bulldozer (using 250 foot pounds of torque)? Or just smaller jobs on a bicycle or lawnmower perhaps? Choose a torque wrench that will adequately cover your anticipated torque specifications by selecting one with an appropriate scale for your requirements. Torque wrenches are most accurate when used within the range of from 20 percent to 95 percent of their indicated scale. So if your normal torque job requires 38 foot pounds of torque, do not chose a torque wrench with a scale from 60 foot pounds to 300 foot pounds of torque.
Look at the torque wrenches that meet your requirements so far. Do they have the ability to utilize both 3/8 inch and 1/2 inch drive sockets? Make sure that the wrench you select will work with the sockets you use. If your normal torque job will use 3/8 inch drive sockets, do not choose a torque wrench that uses a 5/8 inch drive head (where the socket gets attached to the torque wrench).
Consider your normal working conditions. Will you be able to visually read the torque wrench while applying torque? Or will you be beneath a machine in a dark cramped location, such as a car in a garage, and will need to rely on the audible signal generated by the torque wrench instead of a visual reading? Look at the torque wrenches that meet your requirements after completing step two. Does it have the display type you will be relying on most (visual information, or audible clicking confirmation of desired torque being attained)? Choose a torque wrench that has the display you expect to use the most.
Confirm that the torque wrenches that are are potentially available for your use after completing step three are equipped with with proper scales for your routine usage. Are most of your torquing jobs quoted to you in foot pounds, or in metric measurements? Be sure that the torque wrench you select has either a dual scale (SAE and metric readings), or at least a single scale in your preferred numeric system.
Decide how much you want to spend on a torque wrench that meets the four selection criteria. Most torque wrenches will last a lifetime (and indeed are warranted as such) if properly maintained. Remember that initial cost must be offset by the expected useful life of the tool. Will you use and properly maintain it for many years, or are you just working on a current job that requires one? Ultimately, the cost factor may be rationalized either up or down significantly based on usage throughout the tool's lifetime.