Nuts and Bolts: The Lowdown

They may be small but you would be hard pressed to find any machine structure that didn't have them. Bolts may seem like they were invented at the dawn of time. However the functionality bolts provide as one of the most used fasteners is unparalleled.

Fasteners can be defined as objects that hold one object to another.

Fasteners cover everything from nails to rivets and bolts. A phone is held together with about 75 fasteners, a car with 3,500, and a jet plane with 1,500,000. The SR-71 Mach 3 spy plane is built of titanium. And yes, it does have nuts and bolts, and they are all made of titanium.

In the USA, about 600 companies make fasteners. They employ about 60,000 workers, and make about 250 billion fasteners each year, bolts included.

In an average product, about 50% of the total production time is spent fastening parts together. Fasteners such as bolts take up about 5% of the total production cost, but when you add the cost of attaching these fasteners, about 30% of the final cost is used.

Threaded fasteners, which include common nuts and bolts, serve one primary function. They need to be able to provide enough holding force to withstand any external pressure applied to them, like weight or moving forces. It is interesting to note that the often taken-for-granted bolt actually has tons of mathematical formulas attached to its use.

The Romans invented the first screws to fasten wooden parts together. The wood screws were either bronze or silver. The threads were made through filing, or by soldering on a wire wound in a spiral. But the screw was lost with the fall of the Roman Empire. The next reference to screws came in the early 1400's.

In the late 1400's, John Guttenberg used screws in his famous printing press. Apparently, nobody noticed Leonardo Da Vinci's designs from the late 1400's for screw-cutting machines, because first machine to cut screws was built in 1568 by the French mathematician, Jaques Besson.

In the 1400's the bolt made its debut. Bolts are basically just screws that had straight sides and had blund ends. The nut, the bolt's partner in crime was hand-made and very crude. There was no standard for the creation of such. Early engineers had to go through a mound of nuts and bolts to see if any matched each other.

During the Industrial Revolution, threaded fasteners proved that products could be assembled faster and easier if they were used. The next big step came in 1801, when lathes improved to the point of being able to produce matching nuts and bolts.

The next invention was by Henry Maudsley, an English inventor. He built a lathe that could cut screws of any diameter and pitch (the pitch is the distance from one tiny hill on the thread, to the next tiny hill). Between 1800 and 1810, his invention turned the relatively benign art of nuts and bolts into a serious engineering science.

But there was still one more problem. Uniform standards for the shape of fastener threads - the little hills and valleys and sizes - did not exist. In 1841, Joseph Whitworth delivered his paper A Uniform System of Screw-Threads to the Institution of Civil Engineers. This paper described the ideal pitch, depth and shape of the thread. He also specified that the angle between the threads should be 55 degrees.

Without nuts and bolts, many industries would have a hard time keeping things together. For the mechanic, the right supply of nuts and bolts is critical. He cannot leave home without them.