Date Published:May. 10. 2016

Property of Screws with Special Surface Treatment

Property of Screws with Special Surface Treatment

Comparison of axial force generated by difference of surface treatment

Surface treatment
Tightening torque
Axial force
With no surface treatment
5 146 2.3
Fluorine coating
5 317 5.0
Molybdenum disulfide coating 5 425 6.7
Low temperature black chrome treatment
5 584 9.2
PTFE Coating
5 552 8.7
Gold coating
5 273 4.3


Test sample:Stainless steel hex socket head cap screw M5×25
Tensile strength ranking:A2-70

  • Values in chart are for reference only. They are not guaranteed values.
  • Permanent elongation 0.2% of tensile strength ranking A2 - 70 is 450N/mm2. It is recommended to use axial force with which the stress during tightening is 70% or below of 0.2% durability.

Causes of seizing and sticking include frictional heat generated on the thread surface during tightening.
It can be confirmed from the above test results that the reducing the friction coefficient on thread surface by special surface treatment will achieve higher axial force than screws with no surface treatment subject to the same tightening torque. As a result, it is possible to suppress the frictional heat with smaller tightening torque to prevent seizure and sticking.

Comparison of spectral reflectivity generated by difference of surface treatment

Spectral reflectivity of low temperature black chrome treatment and stainless steel black is extremely low and optimal for optical equipment that requires prevent irregular reflection.

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