Technical Guide: Working Principle, Selection and Installation of Self-Locking Fastening Nuts
Loosening of threaded connections caused by continuous vibration is one of the common hidden dangers in mechanical equipment and steel structure engineering. Ordinary flat nuts may gradually rotate and loosen under alternating vibration load, which will reduce the pre-tightening force and even lead to connection failure. Self-locking nuts are designed to solve this problem. This technical document introduces mainstream self-locking nut types, locking mechanism, selection rules and key installation precautions, helping engineers and procurement personnel select suitable anti-loosening nuts for equipment and construction projects.
Main Types and Locking Principle of Self-Locking Nuts
The most widely used types include nylon insert lock nuts, all-metal prevailing torque lock nuts and serrated flange lock nuts. Each type has different anti-loosening mechanism and applicable scenarios.
Nylon insert lock nuts have a non-metallic nylon ring at the top. When the bolt is screwed into the nut, the nylon ring is elastically deformed, generating continuous friction force between threads. This friction prevents the nut from rotating freely under vibration. This nut works well under medium vibration and normal temperature environment, low cost and convenient installation. But it cannot be used in high-temperature working conditions, as high temperature will damage the nylon insert and lose locking effect.
All-metal prevailing torque lock nuts rely on pre-deformed thread structure. During assembly, the bolt needs to overcome the preset torque of the deformed thread to complete screwing. The elastic deformation of metal threads creates persistent friction resistance. It can adapt to high temperature and low temperature environments, suitable for heavy-load and high-vibration equipment, and is widely adopted in engineering export projects.
Serrated flange lock nuts depend on the friction between serrated flange and the contact surface. After tightening, the tooth pattern bites into the contact surface to prevent rotation. It is usually used on flat metal surfaces, simple structure, but the anti-loosening performance will decrease if the contact surface is soft or uneven.
Selection Reference for Self-Locking Nuts
- Temperature condition: Avoid nylon lock nuts above 120℃; choose all-metal lock nuts for high or ultra-low temperature scenarios.
- Load level: Heavy-load structural connection selects high-strength grade 8 or grade10 all-metal self-locking nuts.
- Repeated disassembly: Nylon insert nuts are not recommended for repeated assembly; all-metal lock nuts can bear limited repeated disassembly.
- Surface protection: Select electroplating, Dacromet or passivation treatment according to anti-corrosion requirement.
Key Installation Notes
Self-locking nuts cannot automatically compensate insufficient pre-tightening force. Users must tighten the nut to the specified torque. Too small pre-torque will still cause loosening risk. The thread should be clean without burr, rust or debris before assembly. Do not use excessive lubricant on nylon lock nuts, otherwise it will reduce friction and weaken locking performance. When disassembling, if the nylon ring is seriously damaged, the nylon lock nut must be replaced with a new one during reassembly.
Correct selection and standard installation of self-locking nuts can greatly improve the reliability of threaded connections under vibration. In equipment maintenance and new construction projects, engineers should combine working temperature, load, vibration intensity and material environment to pick the right lock nut type, so as to avoid safety risks caused by loose fastener connections.
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Consult JLFastener technical team for self-locking nut parameter matching and torque reference according to your working conditions.