5 Facts About Fasteners


Learning something new or fascinating about a subject you thought you knew everything about is still exciting. Okay, so fasteners are pretty straightforward, right? Continue reading for some fastener information that may be confusing to you!

Fact 1

If you’ve ever made a part with a tapped location, you’ve probably wondered, “How many threads do I need to tightly connect?” The truth is that it depends but at most, six. Each thread is charged differently because bolts expand slightly when loaded. When a threaded fastener is subjected to tensile stress, the first thread at the connection point receives the maximum load ratio. As shown in the table below, the load on each thread decreases from there. External threads after the sixth don’t distribute the load further and won’t reinforce the connection.

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Fact 2

It is widely assumed that black-oxide alloy steel sockets’ head cap screws (SHCS) are ‘grade 8.’ It is claimed that grade 8 fasteners are so common that the name has become synonymous with all high-intensity fasteners. To be considered ‘grade 8,’ a fastener must meet market requirements for specific characteristics. The ‘class 8’ rating is incompatible with three of the most important physical properties of SHCS: tensile tension, stiffness, and bolt handle labelling. SHCS is far superior to ‘level 8’ and shares many characteristics with Grade 9 fasteners.

Fact 3

When fatigue loading is applied to a bolted attachment, tighten the bolt to its yielding level for maximum strength. If the tensile force added is greater than the compressive intensity of the attachment, a bolt can undergo zero load shift. As a result, a firmly fastened attachment is better suited to handle fatigue load than a loose link because the bolt itself does not experience fatigue load, only the continuous stress exerted by the clamping of the joint. To ensure that the attachment is properly fastened, look up the required torque for a given type of fastener in a table like the one shown here.

Fact 4

Have you ever seen a fastener with a 2A or 3B ranking and wondered what it meant? The number-letter combination denotes the fastener’s thread type. Such scores are clearance fits, meaning they are installed without interruption. Classes 1A and 1B are rarely used, but they are a viable option when quick assembly and disassembly are required. The 2A and 2B thread classes are the most popular because they offer a good price-quality ratio. 3A and 3B are better suited for applications requiring close tolerances and a strong link. Socket caps and socket screws are typically class 3A.

Fact 5

All fasteners can be used on coarse or fine fabric, and each option has distinct advantages. Fine-threaded bolts have larger stress areas than coarse-threaded bolts of the same width, so choose a fine thread for better strength if the bolt’s scale is limited due to dimensional constraints. For threading a thin-walled part, even fine threads are a safer option. You tend to use their higher thread count per inch because you don’t have much space to work with. Fine threads frequently allow for greater change precision by allowing further rotations to travel linearly.

On the other hand, loosely threaded bolts are less prone to be cross threaded during design. We allow for faster assembly and disassembly, so choose these if you frequently reassemble a part. When threads are exposed to rough environments or contaminants, a strongly threaded fastener should be used for thicker placement or coating.



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