This article needs additional citations for. Unsourced material may be challenged and removed. (April 2015) () A torque wrench is a used to apply precisely a specific to a such as a. It is usually in the form of a with special internal mechanisms. It was invented by Conrad Bahr in 1918 while working for the New York City Water Department.

It was designed to prevent overtightening bolts on water main and steam pipe repairs underground [ ]. A torque wrench is used where the tightness of and bolts is crucial. It allows the operator to measure the applied to the fastener so it can be matched to the specifications for a particular application. This permits proper and of all parts.

A torque wrench measures torque as a proxy for bolt tension. The technique suffers from inaccuracy due to inconsistent or uncalibrated friction between the fastener and its mating hole. Measuring bolt tension (indirectly via bolt stretch) is actually what is desired, but often torque is the only practical which can be made. And torque wrenches have similar purposes and mechanisms.

Detailed view of the torque display scale on a beam type torque wrench. This shows a torque of about 160 in.lbf or 18 Nm. The most basic form of torque wrench consists of two beams. The first is a used to apply the torque to the fastener being tightened and serves also as the handle of the tool. Stage Plot Pro Serial Number Windows on this page.

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When force is applied to the handle it will predictably and proportionally with said force in accordance with Hooke's law. The second beam is only attached at one end to the wrench head and free on its other, this serves as the indicator beam. Both of these beams run parallel to each other when the tool is at rest, with the indicator beam usually on top. The indicator beam's free end is free to travel over a calibrated scale attached to the lever or handle, marked in units of torque. When the wrench is used to apply torque, the lever bends and the indicating beam stays straight. Thus the end of the indicating beam points to the magnitude of the torque that is currently being applied.

This type of wrench is simple, inherently accurate, and inexpensive. The beam type torque wrench was developed in the late 1920s/early 1930s by for the Chrysler Corporation and a company known as Micromatic Hone.

Paul Allen Sturtevant—a sales representative for the Cedar Rapids Engineering Company at that time—was licensed by Chrysler to manufacture his invention. Sturtevant patented the torque wrench in 1938 and became the first individual to sell torque wrenches.

[ ] A more sophisticated variation of the beam type torque wrench has a dial gauge indicator on its body that can be configured to give a visual indication, or electrical indication, or both when a preset torque is reached. Deflecting beam [ ] The dual-signal deflecting beam torque wrench was patented by the Australian company in 1948. It employs the principle of applying torque to a deflecting beam rather than a coil spring. This is claimed to help prolong the accuracy of the wrench throughout its working life, with a greater safety margin on maximum loading and provides more consistent and accurate readings throughout the range of each wrench. The operator can both hear the signal click and see a visible indicator when the desired torque is reached. Simplified diagram of a deflecting beam torque wrench.

The wrench functions in the same general way as an ordinary beam torque wrench. There are two beams both connected to the head end but only one through which torque is applied. The load carrying beam is straight and runs from head to handle, it deflects when torque is applied. The other beam (indicating beam) runs directly above the deflecting beam for about half of the length then bends away to the side at an angle from the deflecting beam. The indicating beam retains its orientation and shape during operation, because of this there is relative displacement between the two beams. The deflecting beam torque wrench differs from the ordinary beam torque wrench in how it utilises this relative displacement. Attached to the deflecting beam is a scale and onto that is fitted a wedge which can be slid along the length of the scale parallel to the flexing beam, this wedge is used to set the desired torque.