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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). If the pitch is the normally used "coarse" pitch listed in ISO 261 or ...
Machine screws with different thread diameters Hex key set with metric sizes from 2 mm to 10 mm according to sizes for use with ISO 262 screw sizes (except 3.5 mm for M6 internal set screw) For each size bolt or screw and type of head, there is a corresponding size driver prescribed by various ISO standards, including:
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.
If the thread does not use the normal coarse pitch (e.g. 1.25 mm in the case of M8), then the pitch in millimeters is also appended with a multiplication sign (e.g. "M8×1" if the screw thread has an outer diameter of 8 mm and advances by 1 mm per 360° rotation). The nominal diameter of a metric screw is the outer diameter of the thread.
In 1913, Woolley and Meredith defined them like Anthony, but gave the following dimensions: hex head cap screws up to and including 7 ⁄ 16 inch (11.1125 mm) have a head that is 3 ⁄ 16 inch (4.7625 mm) larger than the shank diameter; screws greater than 1 ⁄ 2 inch (12.7 mm) in diameter have a head that is 1 ⁄ 4 inch (6.35 mm) larger than ...
For example, “.750-10 UNC-2A” is male (A) with a nominal major diameter of 0.750 inches, 10 threads per inch, and a class-2 fit; “.500-20 UNF-1B” would be female (B) with a 0.500-inch nominal major diameter, 20 threads per inch, and a class-1 fit. An arrow points from this designation to the surface in question. [19]
The major diameter may be slightly different from the shank diameter, which is the diameter of the unthreaded part of the screw. The diameters are sometimes given approximately in fractions of an inch (e.g. the major diameter of a #6 screw is 0.1380 in, approximately 9 ⁄ 64 in = 0.140625 in. The pitch P is the distance between thread peaks.
The #6-32 UNC screw has a thread pitch of 1/32 in (0.031250 inches (0.7938 mm)). The #6-32 UNC is a UTS screw specifying a major thread diameter of #6 which is defined as 0.1380 inches (3.51 mm); and 32 tpi (threads per inch) which equates to a thread pitch of 0.031250 inches (0.7938 mm). The optional UNC specification indicates the standard ...