Why Bolts and Nuts are Hexagonal?

Nuts and bolts are both common fastener types for countless assemblies, allowing for components to be clamped between the tightened fasteners to secure them in place. As threaded fasteners that mate together, the bolt is passed through preformed holes while the nut is tightened onto the tail-end of the bolt to maintain an assembly. Whether one is using anchor bolts, carriage bolt parts, or other variations, one may notice that a majority of bolts and nuts feature a hexagonal shape. While this may be attributed to a degree of standardization, such shapes also promote an ease of installation.

As per their naming, hexagonal threaded fasteners are those that feature six sides on their head. With this exact configuration, turning the bolt or nut becomes much easier as the fastener only requires a one-sixth turn before the following flat parallel is reached. To best understand why this is a crucial advantage, it can be useful to understand the difference between a hexagonal design and other common shapes. With a square shaped bolt, for example, the fastener must be turned one-quarter of a rotation every time in order to reach the next flat parallel. As such, flat parallels can only be reached every 90 degrees, as compared to the 30 degree turn requirement of a hexagonal fastener. With fasteners that have more than six sides, on the other hand, the frequency of flat parallels and their size can actually be detrimental. Generally, more than six sides will decrease the efficiency of tools in regard to achieving torque, and such components often face increased rates of breaking or fracturing.

Due to the various benefits of hexagonal shapes, bolts and nuts with such head designs have become universally accepted across the globe. For applications ranging from furniture construction to aircraft assembly, hexagonal threaded fasteners have become widespread. Additionally, the tools that are relied on for installation have followed suit, many tools featuring hexagonal recesses or jaws that are fit for achieving a tight grip around a fastener. While bolts and nuts can be procured in a wide variety of shapes and sizes, there is no shape that surpasses the popularity of the hexagonal head on the market.

Another common head design is the hexagon insert, that of which is when a fastener features a rounded head with a hexagon insert on the top surface. Rather than using equipment that grips the outer sides of the fastener, a tool such as an Allen key is inserted into the recess and will grip the component from the inside. This then allows for torque to be provided through turning, making installation and removal quite easy. Generally, these non-standard socket fasteners are used for applications such as furniture assembly, bicycle construction, and much more.


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