Square head bolts are a type of fastener distinguished by their four-sided, angular heads, providing a robust surface for wrench or spanner grip. Their design allows for high torque application during tightening, making them ideal for heavy-duty applications where strong, reliable connections are required, such as in construction, industrial machinery, and structural assemblies. The flat sides of the square head also prevent rotation when placed against a flat surface, ensuring stability in fixed positions.
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Standard
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Country/Region
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Description
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ISO 4014
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International
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Specifies general requirements for square head bolts in metric series
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DIN 555
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Germany
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Defines the dimensions and properties of square head bolts
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ASME B18.2.1
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USA
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Covers square head bolts in unified inch series
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GB/T 8 - 1988
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China
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Details the product specifications for square head bolts
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JIS B 1180
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Japan
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Japanese standard for square head bolts with specific dimensional tolerances
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Grade
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Material
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Tensile Strength (MPa)
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Application Scenarios
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4.6
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Low-carbon steel (e.g., Q215)
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400/240
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General structural connections in non-critical settings
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4.8
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Low-carbon steel (e.g., Q235)
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400/320
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Common machinery and equipment assembly
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8.8
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Medium-carbon steel (e.g., 45# steel)
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800/640
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Industrial applications, automotive chassis
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10.9
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Alloy steel (e.g., 35CrMo, 42CrMo)
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1000/900
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High-stress environments like heavy machinery and bridges
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12.9
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Alloy steel (e.g., 20MnTiB)
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1200/1080
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Extreme-load scenarios, aerospace and high-performance engines
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A2-70 (Stainless Steel)
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304 stainless steel
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700
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Corrosion-resistant applications in chemical plants
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A4-80 (Stainless Steel)
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316 stainless steel
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800
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Marine and high-corrosion industrial environments
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Treatment Method
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Abbreviation
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Description
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Zinc Plating
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Zn
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Provides basic rust protection; available in different colors (e.g., blue, yellow)
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Hot-Dip Galvanizing
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HDG
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Offers excellent corrosion resistance, suitable for outdoor and heavy-duty use
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Black Oxide Coating
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Black
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Creates a non-reflective, black surface with moderate rust resistance, often used for internal components
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Dacromet Coating
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Dacromet
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Environmentally friendly, chromium-free coating with high corrosion and anti-galling properties
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Nickel Plating
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Ni
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Enhances appearance and provides moderate corrosion resistance for decorative or semi-exposed applications
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Electroplating
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-
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Deposits a thin, uniform layer for improved aesthetics and light corrosion protection
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