Reuse Test: Procedure and Results

The Hardlock Nut can be made of a single material and can be used repeatedly as the preload does not degrade.

A repeat Junker test was conducted 50 times, and the change in the preload is shown in the graphs below. The experimental results (lower graph) from a 51st Junker test confirm no large change in the preload.

Test conditions

Test sample

Bolt: M12 × body 70 mm, strength classification: 4.8, surface treatment: trivalent chromate

Nut: Hardlock Nut, strength classification: 4, surface treatment: trivalent chromate

Test Method

  • (1) Tighten the HLN and commence the tightening test.
  • (2) Subject the fastener to a Junker test to confirm the loosening prevention effect.
  • (3) Next conduct the tightening test.
  • (4) Attach and detach the HLN eight times and then conduct a re-tightening test.
  • (5) Repeat steps 1 to 4 until the nut has been tightened 51 times in step 4.

Tightening Method

Tighten the convex nut to 70% of the yield point.

Tighten the concave nut until firm one-sided contact is made with the convex nut.

Test Schematics

test schematics

Results of the Junker test after the first tightening

results after first tightening

Results of the Junker test after the 51st tightening

results after 51st tightening