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Schematic of a machine tap. Below is a comprehensive drill and tap size chart for all drills and taps: Inch, imperial, and metric, up to 36.5 millimetres (1.44 in) in diameter. In manufactured parts, holes with female screw threads are often needed; they accept male screws to facilitate the building and fastening of a finished assembly.
The half-angle (between the taper surface and the axis of the pipe) is arctan(1 ⁄ 32) ≈ 1.7899° ≈ 1° 47′. The standard for Nominal Pipe Size (often abbreviated NPS, which should not be confused with the abbreviation NPS for the straight thread form standard) is loosely related to the inside diameter of Schedule 40 series of sizes.
where is the tap drill size, is the major diameter of the tap (e.g., 10 mm for a M10×1.5 tap), and pitch is the pitch of the thread (1.5 mm in the case of a standard M10 tap) and so the correct drill size is 8.5 mm. This works for both fine and coarse pitches, and also produces an approximate 75% thread.
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.
Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. [1] " Nominal" refers to pipe in non-specific terms and identifies the diameter of the hole with a non-dimensional number (for example – 2-inch nominal steel pipe" consists of many varieties of steel pipe with the only criterion being a 2.375-inch (60.3 mm) outside ...
In other words the threadform is intentionally truncated by, for example, drilling the minor diameter a bit large with the larger of two possible tap drills. For example, using a 27/64 (.421) as tap drill for ½-13 yields 75% threads (or thereabouts). Using a 7/16 (.437) as tap drill for ½-13 yields 60% threads (or thereabouts).
British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external thread with an internal (female) thread.
The thread form is slightly modified to increase the minor diameter, and thus the strength of screws and taps. The major diameter still extends to within 1 / 8 H of the theoretical sharp V, but the total depth of the thread is reduced 4% from 5 / 8 H = 5 / 8 cos(30°) P ≈ 0.541P to 0.52P. [5]