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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] This increases the amount of the theoretical sharp V which is cut off at the minor diameter by 10% from 0.25H to 7 / 8 − 0. ...
ASME B1.5-1997 (R2014) Acme Screw Threads: Trapezoidal Thread Form: Tr 60×9 ANSI/ASME B1.9-1973 (R2017) Buttress Inch Screw Threads: Breech-Lock Thread Form: ASME B1.10M-2004 (R2014) Unified Miniature Screw Threads: V Thread Form: 0.60 UNM ANSI/ASME B1.11-1958 (R2016) Microscope Objective Thread: V Thread Form ASME B1.13M-2005 (R2015)
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 coarse thread version at 1.5 mm pitch and a fine thread version at 1.25 mm pitch.
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).
Example (metric fine): For M7.0×0.5, major minus pitch yields 6.5, which at 92.9% happens to be an example that pushes over the outer bound of the 90% ± 2 pp, but major minus pitch is still valid, although smaller drills (6.3 mm, 1 ⁄ 4, 6.4 mm) will work well.
Two spanners, both nominal size 5 ⁄ 8 in, with a diagram superimposed to show the logic that allows them both to be nominal size 5 ⁄ 8 in when their actual sizes are clearly different (across-flats distance vs screw diameter). The across-flats definition is the common standard today, and has been for many decades.
[5] 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]
For example, AN6 bolt has a 3 ⁄ 8-24 thread [3] whereas an -6 AN fitting has a 9 ⁄ 16-18 thread. [ 4 ] Originally parts were made compliant to the specification MIL-F-5509, but they are now controlled under SAE AS (Aerospace Standards) specifications AS4841 through AS4843 and AS4875.