Despite what you might believe about the properties of metal, bolts are actually elastic. It's not quite stretch-arm-strong dramatic, but when a critical bolt is tightened to its correct specs, it's actually being pulled beyond its original length. Based on the quality of steel used in the fastener, the diameter of the fastener and how far you stretch it, the load or force applied to the joint, in other words, the two pieces being fastened together, changes. The basic physics of all threaded fasteners are the same. Since metal is elastic, a clamping load is generated. The friction between the threads, bolt shoulders, and even the washers creates additional clamping loads and friction to ensure the bolt is not turned and loosened. These loads are generated by the torque from the technician's tools. How much the faster stretches is dependent on how much torque is applied. If too little torque is applied, the fastener won't generate enough clamping load and the assembly will come apart. If too much torque is applied, the fastener will snap or become elongated to the point where the geometry of the thread's changes and it won't stay torqued. Under the hood, the phrase torque to yield is well understood. With connecting rod bolts and cylinder head bolts and studs, the practice of following torque to yield procedures is followed as standard operating procedure. Head bolts are under tremendous stress from the combustion process and must withstand incredible loads to keep the cylinder head sealed tightly against the head gasket and block. Head bolts may actually have to handle loads of more than five tons per bolt at wide open throttle. But what about under the car? These bolts and studs that stretch are becoming more common there as well. Many of today's tie rods, ball joints, and other suspension components actually use torque to yield fasteners. These torque to yield suspension fasteners are becoming more common as OEMs look to reduce unsprung mass in the suspension components. Some ball joints and almost all tie rod ends use a tapered stud and hole with a nut on top to secure the stud to the knuckle. The 7-10 degree angled taper, along with a threaded stud and nut, lock the components together by tensioning the nut and stud. Torque to yield ball joint and tie rod studs have two advantages. First, they can have a smaller footprint, way less, and still apply the same clamping loads. Second, they offer far more consistent and controllable clamping loads. Torque to yield ball joints and tie rods are usually installed dry. Lubricants reduce friction when a bolt is tightened, which increases the torque load on the bolt or stud, potentially overloading and stretching a torque to yield bolt too far, causing it to break. The increased torque can also cause the female part of the taper to crack as too much clamping forces applied. The first word in torque to yield is torque, and you must do the job right using the right tools. Some components like aluminum knuckles, upper control arms and ball joints can be damaged if not tightened using the correct procedure. Knuckles and upper control arms are aluminum and can be damaged if a torque wrench and torque angle gauge are not used. The torque specifications for components are much more exact now, just look at any service bulletin. Fastener requirements mean many nuts and bolts are more vehicle specific, so using the right part is critical, and hoping to simply replace one that was inadvertently damaged may not be as easy as you think. The bottom line for your customers is no matter how close they think they are to perfect, if their torque wrench isn't accurately calibrated, they'll never know how far off they are in either direction while installing the parts. Following proper procedures will help them avoid these potential problems. Thanks for watching.