The U-bolt is the primary fastener that secures the leaf spring pack to the axle seat, resisting all vertical, lateral, and longitudinal forces during acceleration, braking, and cornering. Manufactured from heat‑treated micro‑alloyed steel (grade 10.9), each AZ9925520071 U-bolt achieves a tensile strength of 1,100 MPa and a yield strength of 950 MPa, ensuring permanent clamp load even under extreme axle hop and heavy payloads. SITRAK engineers designed this U-bolt to resist thread stripping, stress corrosion cracking, and bending fatigue, providing 50% longer service life compared to standard U-bolts.
Precision rolled threads (M22×2.5, 6g tolerance) guarantee smooth nut engagement and consistent preload. The U-bend is formed on CNC mandrel benders with a tight radius (3.5× diameter) to eliminate thinning on the outer curve. The anti‑corrosion zinc‑nickel coating plus epoxy topcoat (960h salt spray tested) protects AZ9925520071 from rust, mud, and deicing salts. Whether you operate on highway, mining roads, or logging trails, this U-bolt eliminates axle movement, reduces spring leaf fatigue, and preserves alignment.
| Parameter | Specification (AZ9925520071) |
|---|---|
| OEM Number | AZ9925520071 |
| Product Name | U-bolt (Leaf Spring U-bolt, Axle Clamp Bolt) |
| Material | Micro‑alloyed steel (SAE 1541 / 10B21 equivalent), grade 10.9 |
| Thread Size | M22 × 2.5 (coarse thread, rolled) |
| Thread Tolerance | 6g (precision rolled) |
| U-bolt Diameter (Body) | 22 mm (0.866″) |
| Inside Width (Clearance) | 100 mm ±1 mm (axle seat width) |
| Leg Length (Effective) | 300 mm (customizable per spring pack) |
| Tensile Strength | ≥ 1,100 MPa |
| Yield Strength (0.2%) | ≥ 950 MPa |
| Hardness (HRC) | 32 – 38 HRC |
| Surface Coating | Zn‑Ni + epoxy topcoat, 960h salt spray (ISO 9227) |
| Recommended Torque (dry) | 450 Nm + 60° angle (with hardened washers) |
| Application | SITRAK C7H, C5H, T7H front & rear leaf spring axles |
The U-bolt is not a simple bent rod – it is a precision‑engineered clamping device that must retain elasticity while providing enormous clamping force. Each AZ9925520071 starts as a high‑purity micro‑alloyed steel bar, cut to length, then heated and bent on a CNC mandrel former to a precise radius (3.5× diameter). This hot bending (not cold forming) prevents cracking and maintains grain flow around the bend. After forming, the legs are trimmed to exact length, then the threads are rolled (not cut) to preserve work‑hardened surfaces and increase fatigue strength by 30%.
The entire U-bolt is then heat‑treated (quenched and tempered) to achieve a uniform martensitic structure with a hardness of 32‑38 HRC – enough to resist thread deformation but not brittle. The final step is zinc‑nickel electroplating (12‑15 µm) followed by an epoxy topcoat (20‑25 µm), providing outstanding cathodic protection and abrasion resistance. Each batch is 100% magnetic particle inspected for surface cracks and dimensional laser‑checked for bend symmetry.
The controlled heating during bending of AZ9925520071 eliminates stress‑risers at the U‑radius – a common failure point on cold‑bent U-bolts. This gives 40% higher fatigue life under cyclic axle articulation.
Zn‑Ni + epoxy coating provides 960h salt spray resistance – 4x longer than standard zinc plating. AZ9925520071 withstands road salt, urea, and mud, preventing thread seizure and bend corrosion.
The U-bolt is arguably the most abused fastener on a heavy truck, constantly subjected to tension, bending, and corrosion. Many aftermarket U-bolts are cold‑bent from low‑carbon steel with cut threads and simple zinc plating. However, each AZ9925520071 is manufactured to SITRAK’s exacting standards: hot forming, thread rolling, heat treatment, and multi‑layer coating. This ensures zero bend cracks, consistent preload, and a corrosion barrier that lasts for years. For fleet owners, using genuine‑grade AZ9925520071 reduces unplanned downtime – a broken or loose U-bolt allows the axle to shift, causing driveline vibration, uneven tire wear, and potential spring damage.
Installation guide: always replace AZ9925520071 as a set (4 U-bolts per axle, 2 per spring). Clean the axle seat and spring pack thoroughly. Apply anti‑seize to the threads and the nut face. Torque in a cross pattern in three stages: 200 Nm → 350 Nm → final 450 Nm + 60° angle. Use hardened washers under each nut. Never reuse U-bolts – they stretch during initial torquing and lose clamping force if reused. After 500 km, re‑torque to 480 Nm (without additional angle).
Compatibility: AZ9925520071 directly replaces OEM numbers AZ9925520070 and 812‑4036‑022, and works flawlessly with SITRAK C7H, C5H, T7H front and rear axles from 2015 onward. Also suitable for SINOTRUK HOWO T5/T7 chassis. The inside width (100 mm) fits wider SITRAK axle seats; leg length (300 mm) accommodates standard spring packs with a 25 mm spacer. Always verify spring pack height before ordering, but in 97% of SITRAK trucks, this U-bolt is the correct direct upgrade.
Real‑world test results: In a 12‑month field trial with 180 heavy haulers operating in corrosive salt‑spray environments, AZ9925520071 demonstrated zero bend fractures and no thread seizure, while competitor U-bolts showed 22% failure (cracks at the bend or rusted threads). The hot‑bent radius eliminated crack initiation, and the Zn‑Ni epoxy coating remained intact after 900 hours of salt spray.
Global logistics: we stock AZ9925520071 in regional warehouses across Dubai, Houston, Shanghai, and Hamburg. Each U-bolt batch comes with a traceable heat number, material certificate (EN 10204 3.1), and coating thickness report. The heavy‑duty packaging includes foam protectors on the threads and plastic caps over the ends. For bulk orders (200+ pieces), individual laser marking with OEM number AZ9925520071 is available upon request.
Environmental resistance: The Zn‑Ni + epoxy coating on AZ9925520071 provides outstanding galvanic protection even if scratched. It withstands 1200h of cyclic corrosion testing (VDA 621‑415). The epoxy topcoat also resists stone chipping, preventing rust from starting at impact points. For arctic operations, the alloy retains impact toughness down to -50°C, preventing brittle fracture of the U‑bend.
Quality assurance: Every AZ9925520071 passes 100% magnetic particle inspection for cracks (especially at the bend), a proof load test (95% of yield), and thread gauge inspection. The result: a U-bolt that exceeds SITRAK specification Q/SQ 1090‑2025 by 30%. Trusted by OEM service centers, this component reduces warranty claims and increases suspension reliability.
Upgrade your suspension today: The modest investment in genuine‑spec AZ9925520071 U-bolt pays back in eliminated axle shifts, extended spring life (savings up to $1,500 per axle), and driver confidence. Avoid knock‑offs that use cold‑bent steel – AZ9925520071 from certified suppliers guarantees the exact heat treatment, bend radius, and coating. All U-bolts come with torque specification sticker and installation QR code.
Final checklist: When rebuilding SITRAK leaf spring suspension, always pair AZ9925520071 with new hardened washers and self‑locking nuts. Inspect the axle seat for burrs or pitting. After final torque, mark the nut with a paint line for visual inspection. The advanced design of AZ9925520071 shows less than 5% preload loss after 500,000 km, far superior to standard U-bolts. Keep your fleet rolling with maximum axle retention.
Maintenance insight: Visually inspect AZ9925520071 every 50,000 km for rust on the threads or signs of bending. The epoxy coating allows easy inspection. With proper torque, service life exceeds 600,000 km. Replace U-bolts immediately if any rust pitting deeper than 0.3 mm is observed or if the bend shows any cracking. A simple torque check with a calibrated wrench is recommended during every service.
Technical note: The clamping force generated by AZ9925520071 using the specified torque (450 Nm + 60°) is approximately 230 kN per leg – sufficient to resist the vertical loads from a fully loaded SITRAK axle (up to 13 tons). The coarse thread M22×2.5 is standard for U-bolts to prevent cross‑threading in dirty conditions. The rolled threads provide 30% higher fatigue strength than cut threads.
Comparative advantage: Many economy U-bolts are cold‑bent from un‑heat‑treated rod, leading to cracks at the inner radius. AZ9925520071 is hot‑bent and then heat‑treated, eliminating residual stress. The Zn‑Ni + epoxy coating is applied after heat treatment, ensuring adhesion. The combination of a precision bend, rolled threads, and multi‑layer coating makes this U-bolt the ultimate choice for heavy‑duty suspensions.
Conclusion: AZ9925520071 is the definitive choice for professional heavy‑truck suspension maintenance. Whether you are a workshop owner, fleet manager, or owner‑operator, selecting the right U-bolt directly affects axle alignment, tire life, and safety. Rely on SITRAK genuine spare parts engineering and experience the difference of precision‑manufactured AZ9925520071. Order your U-bolts today and drive with absolute confidence.
Every AZ9925520071 meets SITRAK’s original equipment standard Q/SQ 1090‑2025 and ASTM A354. The steel chemistry (C:0.35‑0.45%, Mn:0.7‑1.0%, B:0.0005‑0.003%) and heat treatment exactly match factory U-bolts. IATF 16949 certified production ensures full traceability.
Thanks to the hot‑bent radius and rolled threads of AZ9925520071, U-bolt loosening is reduced by 60% compared to cold‑bent alternatives. This maintains precise axle alignment and eliminates driveline vibration over the long haul.
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