My son’s erector set uses square nuts as opposed to the (more common) hex nuts. And so it got me thinking…
Why are almost all nuts and bolt heads hexagons? I work on a lot of old stuff, and I really hate it when I accidently round off the corners of a bolt or nut. I would think it would be more difficult to accidently round off the corners of a square (or even a pentagon) versus a hexagon.
I understand that, when using a standard open-end wrench, it may be difficult (or impossible) to grab onto a square bolt head or square nut since it limits you to only four angles. But how many people use an open-end wrench nowadays? I rarely use mine. I almost always use a ratchet w/ socket or a closed-end wrench. With a square, an eight-point socket or eight-point closed-end wrench should provide adequate angle resolution.
If Wikipedia and my personal impression is to be believed you’ve already given the answer:
The widespread standard of hexagonal nuts and bolt heads is old enough that the frequency of people using open-end wrenches nowadays is irrelevant. Also, for a lot of applications an open-end wrench is the only suitable tool, your experience notwithstanding.
It is a compromise. Early bolts had square heads as they were hand made and squares were simply easier to make. The threads varied with the maker and were individually matched.
In 1841, British toolmaker Joseph Whitworth and his American counterpart, William Sellers of the Franklin Institute proposed creating a system of standardized screw threads. As machinery became smaller and more compact, however, the hex-head bolt evolved to meet the need for more compact bolt heads.
In 1830 James Nasmyth, an assistant to Henry Maudslay, designed a pioneering milling attachment for Maudslay’s bench lathe to make a large batch of hex-head bolts for a scale model they were building for the London Science Museum. By the 1840s, cold-heading machines became available for stamping metal. It took until the 1880s, when Bessemer steel mills began producing the new mild steel in accurate thicknesses and quantity, before cold-heading machines began punching out hex nuts. This innovation meant that nuts stamped from flat metal stock and machined to exact tolerances could be screwed onto bolts made by the new screw-making machines in mills anywhere in the country. Larger hex nuts quickly replaced square bolt heads in heavy industrial applications.