Hardlock Nut


Innovatively designed to withstand loosening from vibration longer than any other fastener on the market, HARDLOCK Nuts are now available in inch sizes. Previously only sold in metric sizes, the makers of the HARDLOCK Nut have responded to North American manufacturer demands for an identical inch-sized version. The HARDLOCK Nut is now available in UNC threads with sizes ranging from ¼” – 1” (in 1/16” increments).    

Loosening occurs in any fastener assembly from repeated vibration and shock because there is a gap between the thread of the bolt and nut. Many self-locking nut systems have been developed worldwide to prevent this loosening (by narrowing the pitch of the screw or inserting nylon in the nut, etc.), but the problem of loosening has not been completely solved by these systems.  In contrast, the HARDLOCK Nut is the only self-locking nut to incorporate the wedge principle used in ancient Japan to almost completely eliminate the loosening of the thread.  The structure of the HARDLOCK Nut is designed to prevent loosening by combining a centered concave top nut and off-centered (eccentric) convex lower nut to form a wedge when tightened. This applies force perpendicular to the bolt, and when the top and bottom nuts are tightened, the self-locking force of the wedge prevents loosening. Therefore, the HARDLOCK Nut maintains an anti-loosening effect, even when subjected to repeated vibrations and shock. The effect of the HARDLOCK Nut has been demonstrated by the results of the NAS (National Aerospace Standard) 3350/3354 Accelerated Vibration Test and Junker Type Transverse Vibration Test, where it significantly outperformed competing self-lock nut systems.    Thanks to the simple design and all-metal construction of the HARDLOCK Nut, it can be used repeatedly while maintaining a strong loosening prevention effect with minimal damage to the thread due to wear. The powerful anti-loosening effect and reusability of the HARDLOCK Nut can significantly reduce maintenance costs associated with frequent inspection and retightening. 

The HARDLOCK Nut can be positioned at any desired point on a bolt and can maintain a strong anti-loosening effect simply by maintaining the torque of the concave nut in accordance to the designated tightening torque. This allows the nut to be fixed strongly in the desired position on the bolt and in places where strong tightening was not previously possible, such as rail joints and rotating and moving parts.    The HARDLOCK Nut it widely used and respected worldwide in various industries including railroad (rail cars and track), building construction, industrial machinery, heavy equipment, and plants (such as oil/gas/energy).    

The HARDLOCK Nut is now available for sale in the following materials and surface finishes:

  • Low carbon steel…ISO Class4/5 equivalent to SAE Grade2 Surface finish…CR3 (Zinc plated trivalent chromate coating)
  • Medium carbon steel…ISO Class8 equivalent to SAE Grade5.
  • Surface finish…Phosphate coating
  • Stainless steel…ISO A2 equivalent to AISI/SAE 304.   


  • now available in inch sizes
  • ¼” – 1” 
  • withstands loosening
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