No the screw

The not of screw , corresponds to the relative distance traversed in translation by a Vis compared to its nut at the time of a full rotation. For example, a screw with a step of 5 (because the " pas" express yourself in mm) will advance of 5 mm during the rotation of a turn for a metric pitch.

Net

A net is a helicoid structure used for the transformation rotation/translation. This structure can be enrouléee around a full cylinder (threaded Tige, for example a screw) or hollow (Trou tapped, for example a nut). The Pas of screw measurement the distance enters a form of the structure and its nearer repetition found by translation according to the axis to the cylinder.

In a mechanism screw and nut, according to the step value of screw, the diameter of the cylinder and the coefficient of friction of materials used,

is rotation alone can involve the translation (Screw fastener)
is the translation alone can involve rotation (handle of screwdriver " automatique")
is the system is reversible

The choice of the Pas of screw (as of the other parameters) thus depends on the considered use. The greatest number of the applications is in the first category (rotation produces the translation, in an irreversible way)

Threading can also meet on cones or truncated cone. They are generally employed that in a zone of engagement of a part threaded mechanical on cylinder (wood screw, with sheet.)

Net with nonmetric step

Before the metric standard ISO is not essential, much manufacturers, in particular Anglo-Saxon, worked out their own standards. The first in this case (in 1841 approximately) was the English engineer Joseph Whitworth. The Whitworth steps, conceived in inches, are still used at the same time to repair the old machines, and when a step more resistant than the ISO standard is necessary. This system exists in thick step (BSW) and fine step (BSF). The included angle is of 55°.

Later, the the United Kingdom standardized the system BA (British Association for the Advancement off Science). The steps were named the odd “2BA”, “4BA” etc, numbers being seldom used. Although different from the steps ISO, the values were defined in metric terms. Thus a “0BA” had a step of 1mm. There are still nowadays uses of the most common steps of this standard in applications of niche. Certain types of mechanics, like the rails of transport of ore, still use this type of step.

The the United States have their own system, called Unified Thread Standard. A version of this standard, called SAE for Society off Automotive Engineers , is used mainly by auto industry étatsunienne. Step SAE is still associated by the public with the fixing in inch, even if American auto industry (and other associated industries) rocked towards the ISO standard since the beginning of the Années 1970.

The screws are described by 4-40, 6-32, 8-32, 10-32, 10-24, etc (for the numerical sizes, the odd numbers are rare), or 1/4" - 20, 1/4" - 28, etc (for sizes in inch), with the first number giving the diameter and the second the many nets per inch .

These steps are sometimes used out of the United States by old models of computers based on the specifications of the IBM PC. Since the essence of computing industry migrated to Asia, it uses the ISO standard.

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