Square Head Bolt

Square head bolts are threaded fasteners with a square head, consisting of a square head and a threaded shank. Their unique square-head design provides a larger contact area for wrenches, offering slip resistance, ease of application, and high torque transmission efficiency. They are particularly suitable for fastening applications in heavy-duty machinery, steel structures, railways, and petrochemical industries—environments characterized by heavy loads, high vibration, and harsh conditions.

Product Description

Square head bolts are threaded fasteners with a square head, consisting of a square head and a threaded shank. Their unique square-head design provides a larger contact area for wrenches, offering slip resistance, ease of application, and high torque transmission efficiency. They are particularly suitable for fastening applications in heavy-duty machinery, steel structures, railways, and petrochemical industries-environments characterized by heavy loads, high vibration, and harsh conditions.

Key Features

Common Materials and Grades

Carbon Steel: Grade 4.8, Grade 8.8, Grade 10.9, Grade 12.9 (High Strength)
Stainless Steel: A2-70, A4-70, A4-80 (Rust-Resistant)
Alloy Steel: SCM435 (High Strength, High Toughness)

Surface Treatments

Galvanized (Blue-White / Yellow / Black), Hot-Dip Galvanized (HDG), Blackening, Dacromet, Nickel / Chrome Plating

Specifications (Common)

1. Metric

Diameter: M5 ~ M72 (Common: M6, M8, M10, M12, M16, M20, M24)
Length: 10 mm to 500 mm
Thread: Full-thread / Partial-thread, standard pitch

GB/T 8 Standard Size Chart (Excerpt)

Specifications	Pitch P (mm)	Head Width S (mm)	Head Thickness K (mm)
M6	1.0	10	4.0
M8	1.25	13	5.3
M10	1.5	16	6.4
M12	1.75	18	7.5
M16	2.0	24	10.0
M20	2.5	30	12.5
M24	3.0	36	15.0

2. Imperial

Diameter: 1/4"–2" (Common sizes: 1/2", 5/8", 3/4", 1")
Length: 5/8"–19"
Thread: UNC, UNF

Applications

Heavy machinery: machine tools, mining equipment, construction machinery
Steel structure engineering: industrial buildings, bridges, towers
Railway tracks: rails, sleepers, switch connections
Petrochemical industry: pipelines, valves, pressure vessels
Power and energy: power plant equipment, transmission towers, wind power equipment

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Standards

Chinese National Standard: GB/T 8-2021 (Square-head bolts)
German Standards: DIN 478 (with shoulder), DIN 479 (short end)
American Standards: ASME B18.2.1

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