Metric Fasteners There are two kinds of ISO metric threads: coarse and fine. The ISO metric thread profile and proportions are under Standards:

 Screw threads are the Whitworth, and the Acme. The Acme thread form has a stronger thread which allows for use in translational applications such as those involving moving heavy machine loads as found on machine tools. Previously square threads with parallel sides were used for the same applications. The square thread form, while strong, is harder to manufacture. It also cannot be compensated for wear unlike an Acme thread .

Screw Hardness and Mechanical Properties:

In addition to Screws and Bolts Dimensional Specifications ,their Chemical properties are among major concerns, such as: Elasticity Measures, Thermal procedures , Atmospheric Conditions, Diagnostic Correctional Methods for different uses and applications. Screws Specifications are based on some Qualitative Standard Measures such as ASTM¹  SAE² ,which are center of attention to this regard.  

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1) DIN = Deutsches Institute Fur Nurmung
2) ISO= International Organization for Standardization
3) ANSI= American National Standards Institute
4) JIS= Japanese Institute Of standards
5) BSW= British Standard whitworth
6) GOST= GOSSTANDART Of Russia’s Standards