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A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter) and the pitch P, both expressed in millimetres and separated by a dash or sometimes the multiplication sign, × (e.g. M8-1.25 or M8×1.25).
For both of these rules of thumb (85%/90% and major minus pitch), the tap drill size yielded is not necessarily the only possible one, but it is a good one for general use. The 85% and 90% rules works best in the range of 1 ⁄ 4 –1 in (6.4–25.4 mm), the sizes most important on many shop floors.
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.
The metric standard used the same thread geometry as the USS standard but differed in that the dimensions and pitch were based on metric units. In 1906, the A.L.A.M developed what would be the SAE thread standard for threaded fasteners based on the USS standard but with a finer thread pitch. [6] [7]
Dimensions of a square thread form. The square thread form is a common screw thread profile, used in high load applications such as leadscrews and jackscrews. It gets its name from the square cross-section of the thread. [1] It is the lowest friction and most efficient thread form, but it is difficult to fabricate.
For example, factory and aftermarket receivers using the Remington 700 footprint are produced with various types of action threads, all with a 26.99 mm (1 + 1 ⁄ 16 in) diameter, but with a pitch of either a 1.588 mm (16 TPI, Remington standard), 1.411 mm (18 TPI) or 1.270 mm (20 TPI, Savage standard).
A size chart illustrating the ANSI sizes. In 1992, the American National Standards Institute adopted ANSI/ASME Y14.1 Decimal Inch Drawing Sheet Size and Format, [1] which defined a regular series of paper sizes based upon the de facto standard 8 + 1 ⁄ 2 in × 11 in "letter" size to which it assigned the designation "ANSI A".
A thread pitch gauge with metric Tr 30 threads (30 mm diameter, 6 mm pitch, tolerance class 7e). In case of the trapezoidal thread form the angle is 30° instead of 29°. [5] [6] All dimensions are in millimeters. [5] [6] Trapezoidal threads are defined as follows by ISO standards: Tr 60×9