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Everything you ever wanted to learn about Nuts and Bolts

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By Bob Wallis (non-engineer)

June

NUTS & BOLTS

My curiosity about the evolution of nuts and bolts, particularly the innovation of threaded fasteners, has always intrigued me. Yes, Joseph Whitworth established fundamental standards for threads, but I found the evolution of bolt head profiles especially compelling.

For a long time, I assumed that square nuts had become obsolete, overtaken by hexagonal ones. It turns out that was a misconception! The hexagon shape emerged as early as the 1800s, with James Nasmith playing a key role in its development, while square nuts lingered on, especially in agricultural machinery. In Australia, manufacturers continued utilizing square mild steel bars for crafting their own nuts well into the 1930s during the Depression. Even now, 1/4" gutter bolts featuring square nuts are still produced.

Traditionally, square nuts were preferred for fastening applications that weren't subjected to tension or alignment issues close to vertical supports. Hexagonal nuts were favored when more precision was necessary. And, in rare instances, octagonal nuts were used in some of the early steam engine designs, although I've yet to see one!

Today, we observe various nut shapes primarily for security purposes. However, kits are now available for their removal! Interestingly, Rolls Royce historically incorporated square nuts even in smaller components like the 3BA size, vital for stabilizing pipe clips. Some railways likewise use square nuts for securing tracks to sleepers.

Bolts are ubiquitous in construction and mechanical design, serving a multitude of purposes—from securing screws in everyday gadgets to anchoring concrete pillars in massive structures. Have you ever stopped to reflect on their origins?

Tracing Back the First Bolt

The history of bolting systems can be traced far back in time, stemming from developments in screws and threads over the last century and a half. While the fundamental concept of threaded fasteners dates back as early as 400 BC, experts focus on the 15th century as a pivotal moment when threaded bolts and nuts became a functional pairing. Frederick E. Graves, in his article on this topic, indicates that this combination was first documented in that period when printed records of screws emerged.

It is interesting to note that although threaded bolts became prevalent in the 15th century, unthreaded bolts had already been in use during Roman times for applications such as securing doors. Graves suggests that the Romans were even adept at crafting the first screws from bronze or silver, utilizing hand-filed threads or wire-wound designs. Additionally, bolt expert Bill Eccles notes the far-reaching history of screw principles traced back to Archimedes, who invented devices to lift water, signaling the start of a long-standing relationship between machinery and fasteners.

Original Uses of Bolts

The narrative can be divided into two eras: the early applications around 400 BC, which included devices like spirals for irrigation, and the integration of screws introduced in the 15th century. By this time, screws had gained traction in various mechanical inventions, including printing presses designed by Johann Gutenberg and tools like clocks and armor. Leonardo da Vinci even conceptualized animal-driven screw-cutting machines during the late 15th and early 16th centuries.

Researchers generally agree that the Industrial Revolution catalyzed the production of nuts and bolts, cementing their place in engineering and construction.

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The Birth of Industrial Bolt Production

According to W.R. Wilbur's “History of the Nut and Bolt Industry in America”, the first bolt-making machine was developed by Besson in France, providing a stepping stone for mass production. American documented histories located in the Carriage Museum reveal that automotive nuts in the early 1800s were noticeably flatter and squarer compared to their later counterparts, which tended toward a chamfered design.

Initially, production of screw threads was manual; however, the growing demand prompted a need for more efficient methods.

By 1845, J and W Wyatt revolutionized bolt production in Britain, but this innovation sparked another complication: varied thread sizes started causing compatibility issues. This led Joseph Whitworth, after extensive research and collaboration with manufacturers, to propose a standardized thread size in 1841 for consistency across the industry.

Standardization of Screw Threads

Whitworth's recommendations included standardizing the angles of thread flanks and the number of threads per inch according to different diameters. Meanwhile, America pursued its own standards and initially adopted Whitworth threads. In the following years, William Sellers would criticize the complexities of the British thread, leading to the development of the American Standard Coarse Series and Fine Series, characterized by their flat roots for easier manufacturing.

The ISO Metric System

During the global conflicts of the 20th century, issues surrounding inconsistent thread standards hampered efforts in allied operations. Consequently, in 1949, countries like Britain, the USA, and Canada agreed upon a Unified thread, effectively merging the best attributes of previous standards for international usability. This led to the current ISO metric threading used worldwide.

Veterans in the field have witnessed significant advancements in bolt technology. “When I first joined the industry three and a half decades ago, bolts were less rigorously tested for strength,” Eccles reflects. “However, with modern standards and enhancements in material technology, the criteria are now much more stringent, resulting in better performance.”

Today, materials for bolts have diversified; we're seeing the introduction of nickel-based alloys suited for high-temperature applications as well as lighter options like aluminum, magnesium, and titanium. Advances have also been made with innovations like wedge-locking systems and hydraulic tensioners, transforming bolt technology across industries, from offshore to energy sectors.

Analysis of connections has also improved substantially over years. “Previously, the choice of fastener size relied heavily on instinct; now we can analyze and test thoroughly before production,” Eccles explains. This strategic approach significantly enhances reliability and performance in crafted products.

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