The Nuts and Bolts of Nuts and Bolts
Super-informative post from MotorCycleCruiser.com
“In technical terms, the job of a threaded fastener is to apply a compressive force to a connection, creating a joint strong enough to oppose any static, tensile, and dynamic loads that may be placed upon it. By that same token, the fastener(s) used must also be capable of resisting impact, shock, vibration, shear, bend, torque and vector (angular) forces, as well as other compressive loads. Boil away the jargon and it means that bolts work by clamping things together under tension and that both the connection and the bolt must be strong enough resist any force that tries to break that connection or the bolt that’s holding it together.
Before we go much further let me point out that while there are formal definitions that distinguish bolts from screws, it’s a lot easier (and just as correct in an informal setting) to use either term to describe threaded fasteners, so unless we need to identify a particular type of fastener, such as sheet metal screw or Allen head bolt, we’ll use the terms screw and bolt interchangeably.
How Bolts Work Steel, no matter what its composition, is elastic, and when a load is applied to it in tension, it stretches; like any other spring, the further it’s stretched, the more it resists. Think of bolts as very stiff springs, and you’ll have the gist of it. Picture two steel plates, held together by a nut and bolt. Turning the nut advances it along the threads of the bolt, which creates tension on the portion of the bolt that passes through the joint, stretching it slightly. The more torque we apply to the nut, the further the bolt stretches, and the harder it tries to return to its relaxed state. As the bolt stretches a compressive load is placed on the joint, binding it together. That compressive load is directly proportional to the distance the bolt is stretched, which itself is dependent on how tight we can make the nut. In a nutshell, that’s how bolts work, and you can now understand why it’s so important to properly torque fasteners. Unless a screw is placed under the proper tension, it won’t be stretched far enough to secure the connection; in effect, it’ll be like any other slack spring-too relaxed to do its job.”
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Source: MotorCycleCruiser.com
