Grade 8 nylon anti-loosening nuts, also known as self-locking nuts, are fasteners that combine the high load-bearing capacity of Grade 8 steel with the elastic anti-loosening properties of nylon. Their core structure consists of a metal nut body with an embedded PA66 nylon ring; anti-loosening is achieved through a threaded interference fit. Designed to be used with Grade 8.8 high-strength bolts, they are widely employed in applications subject to vibration, impact and alternating loads, and represent a key anti-loosening solution for industrial equipment, replacing standard nuts.

Principle of anti-loosening

• The nylon insert forms an interference fit with the bolt threads (standard interference of approximately 0.5 mm for Grade 8 bolts).
• As the bolt is screwed in, the nylon undergoes elastic deformation, generating a sustained radial compressive force that fills the gaps between the threads.
• This creates a stable frictional torque that resists loosening caused by vibration and impact; the anti-loosening reliability is 3–5 times higher than that of ordinary nuts.

Thanks to their combination of high strength and reliable anti-loosening properties, Grade 8 nylon anti-loosening nuts have become standard fittings in the following sectors

• Do not reuse: If the assembly is disassembled and reassembled more than twice, the nut must be replaced, as the nylon ring will suffer permanent loss of elasticity.
• Avoid excessive lubrication: Applying oil to the threads will result in a loss of approximately 60% of the clamping force, affecting the anti-loosening performance.
• Correct orientation: The end of the nylon ring must face the component being connected or the washer; do not fit it the wrong way round.
• Material compatibility: Hot-dip galvanised bolts must be used with nuts produced using the same process to avoid poor fit caused by differences in coating thickness.
• Temperature limits: The long-term operating temperature must not exceed 120°C; otherwise, the nylon ring will soften and fail.