The HARDLOCK Nut is a self-locking nut developed by HARDLOCK Industry through a process of trial and error as an elegant solution to the technical question: “Can the wedge principle be employed for the purpose of loosening prevention?”

In general, forcing a wedge into the gap between a cylinder and its surrounding tube makes it possible to create a powerfully locked assembly (as shown in the figure).

Likewise, creating matching key grooves in both a nut and a bolt, and then using a hammer to drive a wedge into those grooves can be used to produce a powerful self-locking effect. However, this method is unsatisfactory from the standpoint of operability.

The solution employed in the HARDLOCK Nut is to use two nuts to play the roles of the hammer and wedge respectively. A small eccentricity in the sliding part of the convex top surface of the lower nut acts as the wedge. When the upper nut with its concave bottom surface is tightened, the effect produced is exactly the same as that produced by a hammer driving in a wedge. Moreover, it is much more effective to use a screw as this makes it very easy to drive the wedge into place.

This is because when fastened, the HARDLOCK Nut produces stress both in the direction of the axis and in a direction perpendicular to the axis. Firstly, the convex fastening nut generates axial torque in the same way as a normal nut.

Then, as the concave lock nut is tightened, the wedge effect generates stress perpendicular to the axis, which pushes the convex nut against to the screw thread. When the concave nut is completely tightened, the HARDLOCK Nut produces a stable self-locking force by means of the combined stresses of P1 + P2 + P3 (in the figure above), with the result that it remains unaffected by the external vibration or impact.

There is no specific international evaluation method for nut looseness. We perform evaluations by impact and vibration tests in accordance with NAS (National Aerospace Standard) 3350/3354 and Junker screw loosening tests.

Yes. HARDLOCK NUT has been lubricated against galling and seizing.

The HARDLOCK NUT can be used in a wide range of locations including:
• Locations subject to harsh impacts and/or vibration
• Locations where joints are welded or bonded but it is necessary to remove them for maintenance or servicing
• Important locations where post-installation maintenance not feasible
• Dangerous locations involving a hazard to human life
• Locations subject to extreme temperature variations
• Locations where very strong fastening is not possible
• Locations in extremely tough environments

In principle, the HARDLOCK NUT can be reused many times. The actual suitability for reuse will depend on the environmental conditions of previous use, but as long as the nut’s material has not deteriorated or been excessively deformed, its self-tightening performance will not decline.

When considering reusing a nut, remove the concave portion, and then manually screw it in until it touches the convex portion. As long as there is a gap of about one pitch between the two, they can be used again. If there is not an adequate gap, the concave portion may undergo a plastic deformation, rending it unfit for further use.

No. Other threads such as Whitworth, unified screw thread and high-tension specifications are also available.

No. You can use the same commercially available bolts (the old JIS2 class and the new JIS 6g) you use currently. When we make special bolts in-house, they are manufactured to match the nut, but a different in tolerances may result. In this case, the bolt may deviate a great deal from the JIS standard range. Be aware that this may result in the HARDLOCK NUT not fitting in or the concave and convex parts not fitting together as well.

After confirming the material and length of the bolt intended for use, pay attention to the design and ensure that there are at least 2 threads extended beyond the top of the nut assembly.