How to Select Coarse & Fine Thread for Lock Nuts

Automotive fasteners made by precision stamping serve as invisible safety cornerstones for vehicle structures.

In vehicle assembly supporting systems, many manufacturers only focus on the forming accuracy, flatness and anti-corrosion process of stamping parts themselves, while ignoring the adaptability of the thread specifications of lock nuts. Wrong selection of coarse or fine thread will directly lead to: wear of screw holes in precision stamping parts, deformation of sheet metal, excessive assembly clearance, abnormal noise during driving, structural looseness, and even directly reduce the service life of stamping parts, causing structural hidden dangers to the whole vehicle.

1. Coarse Thread: Ideal for Stamped Components for Universal & Efficient Assembly

Coarse thread fits most stamped metal parts with good universality and high assembly tolerance.

• Deeper tooth profile provides strong shear resistance at root and prevents thread slipping.

• Excellent wear resistance, suitable for harsh on-site assembly.

• Recommended for regular stamped sheet metal and rigid structural connections below M10.

2. Fine Thread: For Thin-wall Stamped Parts, Self-locking & Fine Adjustment

Fine thread is designed for thin stamped sheet metal and limited installation space.

• Smaller helix angle under the same diameter brings better static self-locking effect. • Shallow thread cutting reduces cracking risk of thin stamped parts and improves tensile performance.

• Drawback: Shallow teeth tend to wear after repeated assembly, which may cause thread seizure.

• Recommended: Thin-wall stamped structures, sealing adjustment and automotive hardware requiring high self-locking.

3. Common Thread Selection Misconception & Anti-loosening Solution

❌ Misconception: Switching to fine thread can fully eliminate vibration loosening for stamped assemblies.

✅ Engineering Principle: Preload of traditional triangular threads keeps declining under alternating vibration load. Changing pitch alone cannot solve loosening fundamentally.

✅ Preferred Solution:Coarse threads are for structural load-bearing, while fine threads are for precision assembly. Paired with mechanical lock nuts, this design completely eliminates vibration-induced loosening right at the thread structure, safeguarding the long-term precision and structural strength of stamped sheet metal components.

We professionally produce all kinds of automotive metal stamping parts, chassis structural parts and new energy precision stamping components, supporting custom drawing development and mass production. We provide full-process quality control and professional thread matching guidance for vehicle OEMs and auto parts manufacturers.