Fasteners used in automotives

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While any engineer knows the specifications and torque required in automotive manufacturing, the crucial information regarding tightening is rather scarce. Given the high demands placed on today’s technicians and the competition in the industry, it’s no wonder that the fundamentals of bolts and adequate tightening procedures can be overlooked.

Critical problems resulting from loose automotive fasteners

It is necessary to mention that the most common type of fastener used in the car manufacturing industry is the head bolt, followed by the hex-headed cap screw and the stud, the latter being a sort of hybrid between a screw and a bolt. In the eventuality that either of the fasteners comes loose, you will experience problems with your vehicle. For instance, a loose bolt in the engine or transmission area could prevent your car from starting, whereas wobbly fasteners in the suspension or brake system could lead to tragic car accidents.

The risks are eliminated with the right tightening

In order to prevent the aforementioned disasters, engineers make sure the head bolts incorporated in the critical areas are held in tension that exceeds the fasteners’ maximum load and makes sure the joints stay as tight as possible. To be more precise, the automotive fasters are designed to bear loads of between 65% and 90% of their yield strength. In case there isn’t enough tension in the joint, then force and vibration will loosen the bolt relatively easily. On the other hand, excessive tension could damage the fastener just as quickly.

 Tightening should not be confused with torque

Tightening refers to the pressure exerted on the parts clamped by the bolt and its role is to cause the fastener to stretch, as the extension provides the necessary tension to hold the automobile’s parts together. Torque is a term used to describe the rotational force and the primary reason why the screw rotates and creates the desired tension to hold the assembly. Automotive engineers can obtain the ideal tension on small fasteners via torque wrenches and tightening for larger threaded bolts.

Factors that affect the tension resulted from torque

To obtain the proper tension resulted from tightness, technicians must account for the entirety of factors that can alter the tension provided by the torque. First off, as the torque expresses the fastener’s resistance to rotation, adding lubrication will modify the bolt’s ability to provide the necessary tension. To put it simply, lubrication can determine a bolt to exceed its original yield point.

A further noteworthy element that can change the fastener’s ability to provide the desired tension is the installation of a hardened washer. The part can act like a bearing and hence, the fastener can rotate easier and wear out faster. Not utilizing a washer to strengthen the tightness can make the bolt come loose faster in some cases.


The bolts and nuts employed in the car manufacturing industry need to have the same grade, meaning that if you have a 10.9 grade bolt then it is mandatory to tighten it with a 10.9 grade nut. To account for the washer, fastener grading and lubrication, technicians typically refer to the OEM standards.

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