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The common V-thread standards (ISO 261 and Unified Thread Standard) include a coarse pitch and a fine pitch for each major diameter. For example, 1 ⁄ 2-13 belongs to the UNC series (Unified National Coarse) and 1 ⁄ 2-20 belongs to the UNF series (Unified National Fine). Similarly, M10 (10 mm nominal outer diameter) as per ISO 261 has a ...
The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries.
The terms coarse and fine have (in this context) no relation to the manufacturing quality of the thread. In addition to coarse and fine threads, there is another division of extra fine, or superfine threads, with a very fine pitch thread. Superfine pitch metric threads are occasionally used in automotive components, such as suspension struts ...
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.
Example (inch, coarse): For size 7 ⁄ 16 (this is the diameter of the intended screw in fraction form)-14 (this is the number of threads per inch; 14 is considered coarse), 0.437 in × 0.85 = 0.371 in. Therefore, a size 7 ⁄ 16 screw (7 ⁄ 16 ≈ 0.437) with 14 threads per inch (coarse) needs a tap drill with a diameter of about 0.371 inches.
The most commonly used pitch value for each diameter is the coarse pitch. For some diameters, one or two additional fine pitch variants are also specified, for special applications such as threads in thin-walled pipes. ISO metric screw threads are designated by the letter M followed by the major diameter of the thread in millimetres (e.g. M8).
The sealants, where used, are typically thread seal tape thread sealant or a thread seal paste pipe dope (sometimes similar in composition to plumber's putty). Because the thread body is tapered (0.75 in/ft or 62.5 mm/m), a larger diameter keeps compressing into a smaller diameter and finally forms a seal (no clearance remains between the ...
The British Standard Fine (BSF) standard has the same thread angle as the BSW, but has a finer thread pitch and smaller thread depth. This is more like the modern "mechanical" screw [clarification needed] and was used for fine machinery and for steel bolts.