TABLE OF CONTENTS 
What a great invention. Threaded parts have been around for centuries and will likely be with us indefinitely. Threaded parts work well, have numerous uses and are relatively easy to produce.
Historically, standardization has been one of the main stumbling blocks of threaded parts and to some extent is still an issue. In 1918 a number of professional groups in the U.S. got together and settled on a standard that may still be used called the American National Standard. The geometry of the American National thread is easy to work with in that the root and crest measurements are specified as one-eighth of the pitch.
Over time it became obvious that the American National thread had some drawbacks. Namely the tolerances are too tight for easy manufacturing, the threads were not interchangeable with those of other Allied countries until 1948 and there is no provision for tool wear which produces a radius at the root of the thread.
So a group of Oracles from the Allied countries got together and came up with an improved standard called the Unified thread. The Unified thread, which was adopted in December of 1948, is a loosened up, reverse engineered version of the American National thread with a provision for tool wear so that the root and crest of a Unified thread may either have a flat or a flat with radii or a full radius. Parts made to either standard are interchangeable.
Threads made within the tolerances of the American National...
