How to Select Coarse & Fine Thread for Lock Nuts

In the assembly systems of commercial vehicles, construction machinery, and new energy complete vehicles, threaded fasteners are the core safety components with the largest quantity, the widest range of applications, and the highest likelihood of being overlooked. Among them, prevailing torque lock nuts, as the key component to address vibration-induced loosening, are widely used in core load-bearing parts such as chassis, suspension, braking systems, and powertrains.

Statistics from a large volume of after-sales failure data indicate that over 60% of potential thread loosening risks, stripped screw holes, assembly failures and abnormal noise faults stem from mismatched thread selection, rather than product quality issues. Coarse and fine threads have fundamental differences in structural mechanics, self-locking performance, fatigue resistance, assembly tolerance and working condition adaptability; once the wrong type is selected, even high-quality lock nuts cannot completely solve the loosening problem during vehicle operation.

1. Coarse Thread: Universal, Efficient & Tolerant for Rough Assembly

Coarse thread is the standard thread widely used in industry with great universality, interchangeability and fast assembly.

• Larger pitch and deeper tooth profile deliver strong shear resistance at tooth root and anti-slipping performance.

• Good wear resistance and high fault tolerance during disassembly & assembly.

• Application: Preferred for rigid structural connections with specifications M10 and below without special requirements.

2. Fine Thread: High Self-locking for Fine Adjustment & Thin-wall Conditions

As a special design, fine thread compensates the limitations of coarse thread.

• Under the same nominal diameter, smaller pitch and helix angle bring superior static self-locking performance.

• Shallow cutting depth, larger minor diameter cross-section of bolt for higher tensile strength.

• Drawback: Shallow thread is prone to wear. Thread galling or seizure may occur after repeated assembly or uneven load.

• Application: Scenarios requiring high self-locking, fine adjustment, sealing and thin-wall connection.

3. Selection Misconception & Anti-loosening Solution

❌ Common misunderstanding: Simply replacing coarse thread with fine thread can eliminate thread loosening.

✅ Engineering Fact: For traditional 60° triangular threads, radial clearance under alternating vibration and impact load will still lead to rapid preload loss.

✅ Reliable Solution:Equipped with a mechanical locking structure featuring effective torque prevailing nuts, it does not rely on thread pitch self-locking. Instead, it fully counteracts vibration-induced clearances and suppresses preload attenuation through physical thread deformation plus a wedge-shaped locking structure, thus achieving long-term thread locking performance for both coarse and fine threads under all operating conditions.

4. Thread Selection Rules

Choose Coarse Thread Prevailing Torque Nuts:

Commercial vehicle chassis, suspension and brake systems; heavy-load and high-impact working conditions; mass production and frequent maintenance scenarios.

Choose Fine Thread Prevailing Torque Nuts:

Precision electronic assemblies, battery pack structures, thin-wall components, fine adjustment and high-precision sealing positions.

Our company has been deeply engaged in the industrial fasteners and automotive locking components sector for many years, and is capable of supplying a full range of coarse-thread/fine-thread prevailing torque lock nuts in bulk quantities.We provide working condition selection guidance, thread matching solutions, sample testing, small-batch trial orders, mass production, and full-process quality traceability services, to fundamentally solve the problems of incorrect thread selection, loose connections and after-sales rework at the source, and help customers significantly reduce the vehicle's full life cycle operating costs.