High-Strength Wheel Hub Bolt for Automobile Wheels

High-Strength Wheel Hub Bolt for Automobile Wheels — Product Description

The high-strength wheel hub bolt for automobile wheels is the core fastener connecting the wheel to the wheel hub unit bearing, responsible for transmitting the vehicle’s weight and torque loads. In accordance with the T/ZZB 1669-2020 standard, this product applies to round-head wheel hub bolts with a nominal diameter of 12 mm for an operating ambient temperature range of -50 °C to +150 °C, and the standard specifies classification, technical requirements, test methods and quality commitment. According to the heat treatment process, the product is divided into a carburized type and a quenched and tempered type, and common materials include 35K, 40Cr and 35CrMo.

I. Product Features

• Complete strength grade system: The bolt strength grades are divided into 8.8, 10.9 and 12.9, corresponding to the load requirements of mini vehicles, mainstream passenger cars and heavy trucks respectively. Grade 8.8 has a yield strength of about 640 MPa, grade 10.9 about 900 MPa and grade 12.9 can exceed 1100 MPa.
• Clear structural type distinction: Divided into single-head bolts and double-head bolts. Single-head bolts include a knurled spline section and a threaded section, positioned by an interference fit between the knurled spline and the wheel hub hole and widely used in small passenger cars. Double-head bolts have threads at both ends and suit small and medium-sized trucks.
• Reliable anti-loosening design: A conical seat fit or an elastic washer is used, and some vehicle models also adopt a left-hand thread design to enhance anti-loosening performance.
• Standardized heat treatment process: The standard specifies core hardness and tensile strength indicators for the carburized type and the quenched and tempered type respectively, such as a core hardness of 320-350 HV for the carburized type and 34-38 HRC for the quenched and tempered type, with tensile strength covering the range of 1050-1180 MPa.
• Surface anti-corrosion treatment: Processes such as zinc-aluminum coating are used and corrosion resistance must be verified by a salt spray test.

II. Product Advantages

• Load capacity precisely matched to vehicle models: Strength grades from 8.8 to 12.9 cover low-end passenger cars, mainstream passenger cars and heavy trucks, giving a clear selection basis and avoiding overload or excess strength.
• Reliable positioning and anti-rotation: The interference fit between the knurled spline section of the single-head bolt and the wheel hub hole effectively prevents the bolt from turning together during tightening and ensures assembly precision.
• Strong anti-loosening performance: Multiple anti-loosening measures such as the conical seat fit, elastic washer and left-hand thread adapt to continuous vibration and alternating loads during vehicle operation.
• Thorough durability verification: The standard requires torque endurance tests, salt spray tests and several other performance verifications, supported by equipment such as high-frequency fatigue testing machines and universal material testing machines, ensuring reliability under complex working conditions.

III. Application Scope

• Passenger cars and light vehicles: Grade 8.8 and 10.9 bolts suit the wheel connections of mini vehicles, sedans, SUVs and other mainstream passenger cars.
• Heavy trucks and commercial vehicles: Grade 12.9 high-strength bolts are used for heavy trucks, trucks and other models that must withstand large torque loads.
• Small and medium-sized trucks: The double-head bolt structure suits the connection between the wheel hub housing and the tire of small and medium-sized trucks.
• Harsh temperature environments: The bolts work normally within an ambient temperature range of -50 °C to +150 °C, meeting the needs of cold zones and high-temperature regions.
• Repair replacement and original equipment supply: They can be used both for original assembly in automobile manufacturing and as replacement parts for after-sales repair.