Screw threads are almost never made perfectly sharp (no truncation at the crest or root), but instead are truncated, which is known as the thread depth or percentage of thread. The UTS and ISO standards codify the amount of truncation, including tolerance ranges.
A perfectly sharp 60° V-thread will have a depth of thread ("height" from root to crest) equal to 86.6% of the pitch. This fact is intrinsic to the geometry of an equilateral triangle—a direct result of the basic trigonometric functions. It is independent of measurement units (inch vs mm).
The typical depth of UTS and ISO threads with truncation included is around 75% of the pitch. Threads can be (and often are) truncated a bit more, yielding thread depths of 60% to 65%. This makes the thread-cutting easier (yielding shorter cycle times and longer tap and die life) without a large sacrifice in thread strength. For many applications, 60% threads are optimal, and 75% threads are wasteful or "over-engineered" (additional resources were unnecessarily invested in creating them). To truncate the threads further different techniques are used for male and female threads. For male threads, the bar stock is "turned down" some before thread cutting, so that the major diameter is reduced. Likewise, for female threads the stock material is drilled with a slightly larger tap drill, reducing the minor diameter. The pitch diameter is unchanged by these operations which change material dimensions prior to tapping (thread cutting).
A perfectly sharp 60° V-thread will have a depth of thread ("height" from root to crest) equal to 86.6% of the pitch. This fact is intrinsic to the geometry of an equilateral triangle—a direct result of the basic trigonometric functions. It is independent of measurement units (inch vs mm).
The typical depth of UTS and ISO threads with truncation included is around 75% of the pitch. Threads can be (and often are) truncated a bit more, yielding thread depths of 60% to 65%. This makes the thread-cutting easier (yielding shorter cycle times and longer tap and die life) without a large sacrifice in thread strength. For many applications, 60% threads are optimal, and 75% threads are wasteful or "over-engineered" (additional resources were unnecessarily invested in creating them). To truncate the threads further different techniques are used for male and female threads. For male threads, the bar stock is "turned down" some before thread cutting, so that the major diameter is reduced. Likewise, for female threads the stock material is drilled with a slightly larger tap drill, reducing the minor diameter. The pitch diameter is unchanged by these operations which change material dimensions prior to tapping (thread cutting).