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Themetric threads (ormetric ISO thread,isometric
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in,triangular wire) is a thread formed by an equilateral
triangle turns off. The isometric profile is the easiest to achieve.
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Thethread increase, is the relative distance that a screw travels in translation with respect to its nut in one complete turn. A screw with a thread pitch of 1.25 is e.g. B. with a metric pitch in a turn of 1.25 mm more turned.
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Not rough: The baseline should be used first. They are mainly used for screws and for all common uses (ferrous and non-ferrous metals).
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Fine yarn increase: They are used on threads on thin, short tubes
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engagement lengths (low height nuts...), shocks, vibrations and in the case of expensive
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Constructions (automotive, aerospace...) recommended.
Thread Dimensions - Coarse Pitch (NFE 03-014)
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Resistive section = (π / 4) x [ (d2 + d3) / 2]²
Thread dimensions - fine pitch (NFE 03-014)
SISO system for thread tolerances
The tolerance system used for threads is analogous to that for shaft/housing fits. If only the nominal diameter is taken into account during the adjustment, the diameter of the thread crests (Æ d1 or Æ D1) and the pitch diameter (Æ d2 or Æ D2) are affected for the threads, which leads to a double dimensioning .
IT tolerances or tolerance interval
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The value of the tolerance interval is represented by a number (or degrees: from 3 to 9). Values ​​4, 6 and 8 are the most common, with 6 being the most common value for screw connections (ex: 6H/6g). The higher the number, the greater the tolerance.
Values ​​below 6 are recommended for fine or precise finishes and for short, interlocking lengths between threads. Tolerances greater than 6 are recommended for "coarser" requirements with longer mesh lengths.
Deviation (or IT position)
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The position of the tolerance interval is indicated by a lowercase letter for axes, rods or screws (e.g.: e, g, h...) and by an uppercase letter for bushings or tapped holes (G, H.. .) as with adjustments.
 The letters h and H have zero gap. Schematically, an e/H type assembly results in a large clearance, g/H in a small clearance and (h/H) in an assembly with zero clearance.
