Torque is the applied tightness of the retaining bolt without over-tightening (which can mash threads to the mating surfaces) or under-tightening (which can lead to the bolt not holding the component securely enough). A common tool in the automotive repair industry, the torque wrench or similar tools can be used to fix household applications and even electronic repair or assembly. The fact is that any bolt fastening a component may have a recommended torque specification.
The Torque Wrench
There are a couple different designs of torque wrenches that apply a degree of tightness to a hex-head bolt. Once the desired setting of the torque wrench is achieved, the wrench defaults its tightening application. This is so the intended hex-head bolt cannot be over-tightened or under-tightened.
The more common torque wrench is an adjustable model. It features standard foot pounds on one side and Newton meters on the other for metric applications. Setting the desires torque on the wrench comprises of twisting the lower handle that manipulates the length of the shaft on the torque wrench and/or the ratcheting device in the head of the wrench to apply more or less torque. Much like a ratchet, the torque wrench mates to a suitable drive hex-head socket that also matches the size of the hex-head bolt intended to be tightened.
Place the socket attached to the wrench over the hex-head bolt, tighten the bolt in a clockwise motion. Once the torque setting has been achieved, the wrench will default. Most commonly, a clicker torque wrench is favourable. It will click as the ratcheting mechanism in the head fails to tighten the hex-head bolt any further than the preset torque setting.
Other types of torque wrenches come in smaller versions to compute inch-pounds and Newton centimetres for the metric version. These may feature clicker-style alerts or may feature a pivoting ratchet head. Once the desired tightness is achieved on the intended hex-head bolt, the ratcheting head of the torque wrench will pivot slightly. This type of wrench needs to be paid close attention to since it will still allow you to continue tightening the hex-head bolt past the preset torque setting.
Since hex-head bolts are not the only types of bolts that need to be torqued, you can often install other types of adaptors to the torque wrench, provided the correct drive of the adaptor mates to the drive of the wrench. Hex-head bit and Torx-bit adaptors are common types of bolts that require being torqued. These adaptors employ a male applicator to a female bolt head, unlike the hex-head bolt, which receive a female socket.
Types of Torque Wrenches
Other types of torque wrenches use a preset torque setting. These types cannot be used for any other setting than the preset setting the wrench features.
Another type of wrench features a digital or dial indicated reading. Once you have achieved the correct tightness on the hex-head bolt, the digital or dial indicator will alert you that you have achieved the desired torque setting. Much like the pivoting head wrench, care must be applied to these types of wrenches since it will allow you to continue to tighten the bolt beyond the preset torque setting.