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The minor diameter is the lower extreme diameter of the thread. Major diameter minus minor diameter, divided by two, equals the height of the thread. The minor diameter of a nut is its inside diameter. The minor diameter of a bolt can be measured with go/no-go gauges or, directly, with an optical comparator.
American Society of Mechanical Engineers National Pipe Thread Taper (NPT) [5] Nominal pipe size Thread density Thread pitch P Hand-tight engagement [6] Effective thread [6] Overall length L 4 [6] Actual outside diameter D Tap drill; Length L 1 Turns Diameter E 1 Length L 2 Turns Diameter E 2; inch inch −1 inch mm inch inch inch inch inch inch ...
The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch.For diameters smaller than 1 / 4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is an inclined plane wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread.
Because only 5 ⁄ 8 of this height is cut, the difference between major and minor diameters is 5 ⁄ 4 × 0.8660 × P = 1.0825 × P, so the tap drill size can be approximated by subtracting the thread pitch from the major diameter.
However, the top and bottom 1 ⁄ 6 of each of these triangles is cut off, so the actual depth of thread (the difference between major and minor diameters) is 2 ⁄ 3 of that value, or h = p/(3tanΘ) = 0.64032738p. The peaks are further reduced by rounding them with a 2×(90° − Θ) = 180° − 55° = 125° circular arc.
For a taper thread, it is the diameter at the "gauge length" (plus/minus one thread pitch) from the small end of the thread. The taper is 1:16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.
ISO 68-1 doesn't define major and minor diameters (although the major diameter is fairly obvious), only the shape of threads for any particular pitch. For a particular major (ie. nominal) diameter and pitch (as defined, for example in ISO 261), the minor diameter can be calculated: