Over the ages, pipe has evolved from the ceramic and stone pipes of the Roman empire and before, to our modern version, the iron pipe. There are today, of course, countless variations, many of which we hope to explore and explain herein. Our treatment of the subject is by no means an authoritative development of the history of pipe development.
For our purposes the most basic pipe is good old fashioned Iron Pipe.
"Iron Pipe" is a bit of a figure of speech, used because it describes adequately the dimensional characteristics of what we're talking about. That being said, iron pipe (or just plain pipe) can be made out of steel of various grades, stainless steel, and often times brass or bronze, and sometimes copper or plastic.
Be careful about copper and plastic pipe though, because these materials are also broadly used in the manufacture of tubing which (dimensionally speaking) is not pipe. Adding further to the confusion, copper pipe (as opposed to copper tubing) is usually called pipe and, like iron pipe, is size-designated by a "nominal" (or trade size) rather than actual diameter, but using different actual diameters from those of iron pipe. For a fuller explanation, please refer to our Abstract: About Copper Pipe (coming soon).
British vs. American Pipe
As for Iron Pipe, it appears that the world has gone down two roads on pipe standards: The British, and The American. Someone might ask, "Why did the Americans feel the need to muck things up? Why couldn't they just go with the flow and use the British standard like everyone else? This is a good question, to which I have my own answer, based on my personal suspicions and speculations. This is not authoritative, it's just my hunch.
One thing everyone must agree on is that the Americans have historically been pretty good at finding the most economical way of making something that works. It may not be the most elegant, or most excellent, but "it's low-cost, it gets the job done, and it works." This brings us to the crux of the break between British pipe and American pipe... it's the threads (or more particularly, the thread forms)!
Going way back, the British standard for thread-making is the Whitworth thread, which was defined by Joseph Whitwoth. The Whitworth thread is a beautiful thing in its own right. Thing is, it's difficult to cut. So back in the early days of the industrial revolution, an American engineer named William Sellers defined and promoted a standard thread form which was subsequently adopted by all of American industry. And as it turns out, it was a very good standard, and it made thread cutting of matched male- and female-threaded parts much easier than was the case for Whitworth threads. The adoption of this standard was surely helpful to the industry, even though it had the potential of introducing myriad thread compatibility issues with zillions of already-existing hardware items in other places.
But think for a moment about this incompatibility issue... If an American coach builder in the late 1800's had the choice of importing his nuts and bolts from England or buying them from the machine shop in Milwaukee (or even just down the street), which would he choose? Today we can order stuff from China on ebay and it gets here in a few days. But back then importing foreign goods was a whole 'nother issue! It took months. So if we Americans cut different threads to those of the Brits, who cares? I mean, realistically, what difference did it make? It wasn't as though the land was already filled with Range Rovers and Fiats. Compatibility simply wasn't much of an issue. Economics, and cost of manufacture, however, were very real issues.