On Specifications and other historical issues:

The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches. That's an rather odd dimension for such a mundane task as guiding a rolling vehicle. Why is that gauge used? Because that's the way they built them in England, and the US railroads were built by English expatriates.

Why did the English build them like that? Because the first rail lines were built by the same people who built the pre-railroad tramways and that's the gauge they used. Why did they use that gauge? Because the people who built the tramways used the same jigs and tools that they used for building wagons.

Okay! Why did the wagons have that particularly odd wheel spacing? Well, if they used any other spacing, the wagon wheels would break when used on some of the old, rutted, long distance roads in England. So who built those old roads? The first long distance roads in Europe (and England) were built by Imperial Rome for their legions and were used long after that.

And the ruts? The initial ruts, which the wagon builders had to match for fear of destroying their wagon wheels and wagons, were made by Roman war chariots. Since the chariots were made for, or by, Imperial Rome, they were all alike in the matter of wheel spacing.

Thus, we have the answer to the original question. The United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman war chariot which, naturally, were made wide enough to accommodate the back ends of two war horses.

Space Shuttles have two large solid rocket boosters (SRBs) attached to the sides of the main fuel tank. These SRBs are made by Thiokol at their factory in Utah. The engineers who designed the SRBs might have preferred to make them a bit larger in diameter, but the SRBs had to be shipped by train from the factory to the launch site. The railroad line from the factory runs through a tunnel in the mountains and the SRBS have to fit through that tunnel. The tunnel is slightly wider than the railroad track, and, as a result, is somewhat wider than two horses' behinds.

So, a major design feature of what is arguably the world's most advanced transportation system was determined by the width of a horse's ass! Specifications and bureaucracies live forever. The next time you are handed a specification and wonder what horse's ass came up with it, you may be closer to the truth than you think.

Another engineering joke -

There were three Indian squaws.  One slept on a deer skin.  One slept on an elk skin and the third slept on a hippopotamus skin.  All three became pregnant and the first two each had a baby boy.  The one who  slept
on the hippopotamus skin had twin boys.  This goes to prove that the squaw of the hippopotamus is equal to the sons of the squaws of the other two hides.