Testing of Various Types of HARDLOCK Nut

Vibration Impact Test (Horizontal impact) (Vertical impact)

  • Testing data
  • We conducted our own original severe vibration impact tests based on the US NAS3350/3354 standard screw looseness test, and verified that all types of HARDLOCK nuts exceed this evaluation standard by a clear margin. As self-locking nuts used in civil engineering applications such as railways, highways, bridges, pylons, etc., HARDLOCK nuts are exposed to a wide range of vibrations and impacts on a continuing basis. However, the data from these tests proves that HARDLOCK nuts maintain a stable tightened condition regardless of the type of impact to which they are exposed. A performance comparison with other general-purpose nuts demonstrates the clear superiority of HARDLOCK nuts for tasks where vibration resistance is paramount.
    • See video
  • Horizontal Impact TestHorizontal Impact Test
  • Vertical Impact TestVertical Impact Test

Junker horizontal screw looseness test

  • Junker horizontal screw looseness testAfter Director Ohashi of the Japan Research Institute for Screw Threads and Fasteners (and originally from the Shonan Institute of Technology) along with others carried out tests at a variety of angles, we put in the manufacturing request with Iwata Tekkosho. This testing allows confirmation of the degree to which the initial axial force (tightening strength) drops under a variety of parameters, giving the results in both numerical and graph form. While not as extravagant as the NAS3350, this test provides reliable numerical data and has become established in Europe as a method for evaluating screw looseness.
  • Test conditions

    • Tested sizes: M10 to M16

    Amplitude of vibration: ±0.25 mm to ±1.5 mm

    Vibration frequency: 1 to 30 Hz

    Axial force: 1 to 80 kN


pdfThe report for the horizontal screw looseness test by the national agency China Academy of Material Science

Tensile Strength Test

  • No. Test product Breaking load
    1 General-purpose nut 9,050kg
    2 General-purpose nut 8,950kg
    3 HARDLOCK nut 9,800kg
    4 HARDLOCK nut 9,800kg
    Size: HARDLOCK nut M16 X P2.0@Material: SS400
  • Amsler Tensile Test
  • Amsler Tensile TestAmsler Tensile Test

Torque / Axial Force Test

  • Relation between tightening torque and bolt axial force (Relation between tightening torque and bolt axial force)
    Unlike conventional double nuts,with HARDLOCK nuts there is no increase in the axial force applied to the bolt even when the upper (concave) nut is tightened, which means that in the case of HARDLOCK nuts it is possible to control the amount of torque and axial strength. *However, from the point when the gap between the upper and lower nuts completely disappears, the axial force rises slightly. So care should be taken not to over-tighten the upper (concave) nut.
Test sample Test product Size Material Tightening torque Lower nut Upper nut Change in axial force %
No.1 HARDLOCK nut M10~P1.5 SS400 25N/M 1.6 1.6 0
No.2 HARDLOCK nut M10~P1.5 SS400 25N/M 1.45 1.45 0
No.3 Double nut M10~P1.5 SS400 25N/M 1.65 1.8 9
No.4 Double nut M10~P1.5 SS400 25N/M 1.8 2 11
*The tightening torque given here is common to both the upper and lower nuts. In the case of HARDLOCK nuts, the lower nut is a convex nut.

Applied Results Test

This test was carried out by gradually loosening the upper nut from the specified torque condition.
In this test, HARDLOCK nuts maintained their completely connected condition regardless of the environment. This test was conducted based on the assumption that the nuts were not fully tightened during installation. For example, even when loosened by 45 degrees, in the case of an M12 HARDLOCK nut more than half of the tightening torque remained. Moreover, when a vibration test was performed in this condition, no loosening occurred. This result is further evidence that in the case of HARDLOCK nuts, a self-locking effect is exhibited even if the nut is not fully tightened.