1. Overview & Definition
A U-bolt is a U-shaped standard fastener with dual fully threaded straight legs and a semicircular or rectangular curved bottom. It is professionally designed for clamping and fixing cylindrical components, including steel pipes, cable trays, circular steel tubes, vehicle suspension parts and power pole fittings. Different from ordinary hexagonal bolts and double-end studs that only provide planar clamping force, U-bolts adopt encircling clamping structure, featuring uniform stress, strong anti-slip performance and adjustable pre-tightening force, which are widely used in construction, bridge, petrochemical, new energy, automobile and power transmission engineering.
Standard U-bolt assembly includes: U-bolt body, flat washers, high-strength hexagonal nuts. Spring washers are prohibited in heavy-load and vibration working conditions to avoid fastening failure.
2. U-Bolt Structural Schematic & Core Dimensional Parameters
2.1 Structural Visual Schematic (Engineering Standard)
2.2 Key Technical Parameters
Inner Width (W): The inner clear distance between two bolt legs, must match the outer diameter of fixed pipe/steel tube to ensure full fitting and uniform clamping.
Bend Radius (R): Arc radian of U-bottom, consistent with outer diameter of clamped circular parts to avoid local stress concentration.
3. U-Bolt Classification
Round U-Bolt: Semicircular arc bottom, the most widely used type, suitable for all standard round pipes, circular steel tubes and cylindrical accessories.
3.2 Classified by Strength Grade
High-Strength Grade (10.9): Made of 35CrMoA/42CrMoA alloy steel, after quenching and tempering heat treatment, applied for bridge pipeline, wind power auxiliary structure, vehicle suspension and vibration working conditions.
Electro-galvanized: Low cost, thin coating, suitable for indoor dry environment.
Dacromet / Zinc-Aluminum Coating: No hydrogen embrittlement risk, high salt spray resistance, applicable for coastal heavy corrosion and high-strength bolt scenarios.
4. Main Engineering Application Scenarios
U-bolts are used for fixing bridge drainage pipes, cable protection tubes, guardrail bottom brackets and bridge auxiliary steel structures. The encircling clamping method effectively solves the loosening problem caused by bridge vehicle vibration, ensuring long-term stable fastening of pipeline supports.
Standard U-bolts cooperate with pipe supports to fix process pipelines, water supply and drainage pipelines, and thermal insulation pipelines. They can limit pipeline displacement caused by thermal expansion and contraction, and bear lateral and axial auxiliary loads.
Widely used for fixing fan tower auxiliary pipelines, photovoltaic support steel pipes, power pole hardware and cable brackets. High-strength anti-corrosion models adapt to outdoor wind, rain and ultraviolet aging environment.
Professional U-bolts are used for vehicle leaf spring fixing, axle limit clamping and mechanical equipment roller limit, with excellent anti-vibration and anti-loosening performance.
5.1 Pipeline Fixed Installation Section Schematic
Positioning & Fitting: Select U-bolt with matching inner width according to the outer diameter of the fixed pipe to ensure close fitting without gap or extrusion deformation.
Anti-Loosening & Protection: For vibration working conditions, adopt double-nut anti-loosening measure; repair coating damage caused by construction to ensure anti-corrosion performance.
Encircling clamping structure, large contact area, uniform stress and no local pressure damage to pipelines.
Simple structure, convenient installation and maintenance, low later replacement cost.
The inner width of the U-bolt must match the pipe diameter; oversized width will cause shaking, and undersized width will cause extrusion crack.
7. Common Industry Standard Marking
Executive Standards: GB/T 18848, ISO 4032, ASME B18.2.1
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