Humble Inventions #1: Nails and its Derivatives

In her book on the small inventions that make a huge difference, Nuts and Bolts, Roma Agrawal starts with the humble nail:

“The nail enables us to connect things together. That might not sound like much, but the act of joining two things was once radical.”

Complex systems could only be built when we could fasten things together. She includes the derivatives of the nail (rivet, screw, bolt) as part of her description, since all of them “enabled robust connections… at a vast range of scales”.

 

To make nails, one first needed to find metals, understand their properties, and figure ways to shape them. Metals can be hammered straight into other materials; and can be shaped into a sharp point. This isn’t a trivial point – most other materials snap or deform if you hammer them. But to shape metals into nails, humans had to find way to generate very high heat and then invent other tools to hold and beat them.

 

For a long time, nail making was hard (and skilled) work, which meant nails were very valuable. Imagine that!  So much so that in the pre-industrial era, Britain banned its exports to its colonies. Until America’s independence, when it could develop its own industries, when people shifted, they often burnt their houses down to recover those precious nails.

 

Why does a nail have sharp point? So that when you hit it to drive it in, the force get concentrated into a tiny point, which can be enough to push it in. In addition, if all that force is at a tiny point, then the damage to the material into which the nail is being driven is also less. Why doesn’t the nail itself buckle when hit with such force? Because of a strange property of metals – whether they buckle depends not just on the force, but also the duration over which it was applied. With a nail, the duration is very short, not enough for the nail to buckle.

 

What holds a nail in place? Friction with the material. This implies longer nails are better (more area for friction to act), and also that they be encased entirely in the materials they join (if it sticks out, there’d be less friction). It also means that shaking and vibrations would loosen it over time. As you can imagine, in situations where these factors can’t be met, nails are not a good candidate.

 

Those other situations led to the invention of the screw, the rivet and the bolt. The screw’s helical thread means it has to be driven in by rotation (a screwdriver, not a hammer) and it grips the materials more tightly, making it less susceptible to vibrations. A bolt helps fasten things together, reducing the role of friction and the danger of vibrations and shaking.

 

It’s amazing how even something as humble as the nail took so much effort and time to master, engineer and mass produce. And even today, the nail and its variants are so critical in holding things together, from that painting on your wall to parts of aircrafts to bridges to your laptops and phones.

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