Date Published:Jul. 08. 2016

Special Surface Hardened Screws

4 Advantages of Special Surface Hardened Screws

(1) Non-lubricated, yet does not cause seizing

  • Galling and seizing are prevented by curing the screw surface using NBK's own processing technology.
  • There is nothing adhering to the surface, eliminating concerns about contamination due to stripping when tightening.
  • Ideal in environments where contamination must be avoided, such as in manufacturing equipment for semiconductors, FPD, food and medical areas.
  • Unlike screws with untreated surfaces, for which seizing occurred in repeated use and caused breakage, special surface hardened screws are confirmed to be removable without seizing. These special screws also passed the Thread Limit Gauge after the test.

(2) Axial Force Stabilization

The special surface hardened screws ensure proper axial force through tightening torque management.

Variation in Tightening Torque

There is minimal variation between 1 and 10 N・m as compared with screws with untreated surfaces, and small variation in torque coefficient due to repeated use.



Variation in Axial Force

The changes in axial force are compared when repeatedly tightened at a constant tightening torque.

【Untreated Screw】
Axial force drops significantly, and the generated axial force is unstable when controlling screw tightening at a constant torque. High probability of failing to reach the proper axial force in repeated use.

【Special Surface Hardened Scre】
Less change in the axial force, ensuring the proper axial force through tightening torque management even after repeated use.



(3) Usable in High-Temperature Environments

Special surface hardened screws are ideal for preventing seizing in high-temperature environments.
The following test has confirmed that special surface hardened screws can be removed without seizing even at high temperatures.
For conventional screws with surface treatments, the coating may burn, causing seizing or deposition of contamination.

Conventional Surface Treated Screw (Polytetrafluoroethylene)

  • Seizing
  • Contamination

Special Surface Hardened Screw

  • No Seizing
  • No Contamination

Test method: tightening → heating (500°C/8h) → cooling (room temperature) → removal, cycle repeated 5 times

(4) No Design Change Needed

The strength and corrosion resistance of special surface hardened screws have been confirmed to be equal to that of screws with untreated surfaces.
There is no need to make significant design changes, such as size, when replacing your current product.


The tensile strength of special surface hardened screws has been confirmed to be equal to that of screws with untreated surfaces.

Test equipment: Autograph (SHIMADZU AG-100kND)

Corrosion Resistance

The corrosion resistance of special surface hardened screws has been confirmed to be maintained equivalent to that of screws with untreated surfaces.

Test Method : Neutral Salt Spray Test (JIS Z 2371: 2000)
Sample        : SUS316L special surface hardened screw
Test Time    : 168h


  • FPD Production Equipment
  • Food Machinery
  • Semiconductor Production Equipment
  • General Industrial Machines


Special Surface Hardened Screw Products

We recommend screws with a ventilation hole for vacuum applications such as semiconductor equipment.

●Hex Socket Head Cap Screws / Surface Hardening Treatment >>SNSL-PN
●Hex socket Head Cap Screws with Ventilation Hole / Surface Hardening Treatment >>SVSL-PN

Product Introduction Heat resistance/corrosion resistance Seizing Prevention Machine Tools Semiconductor Manufacturing Equipment Food Machinery Automotive Manufacturing Process Medical Equipment FA Devices Special Screws