According to the American Society of Mechanical Engineers website, the
Standard for the Diameter and Overall Dimensions of Pipe and Its
Threaded Ends was adopted in 1886-87.
See:  http://www.asme.org/history/cs_chron.html
Of course, pipe in what became the standard sizes and threads had to
have been produced for quite a while before the formal Standard was
created.  Anybody know how long?

Robert Douglass