SPRON is an SII brand name coined from SPRING MICRON.



“SPRON” is a special metal (Co-Ni alloy) developed for mechanical watch springs, through collaboration with the Institute for Materials Research, Tohoku University.
It has the excellent characteristics of high elasticity, durability, corrosion resistance, and heat resistance allowing to be used in wide-range of fields, including medical materials, small precision springs, as well as springs for watches.



SPRON 100 is a strain age hardening type Co-Ni alloy that makes the most of the work-hardening properties of cobalt-based alloys. High mechanical strength and corrosion resistance combined with excellent precision processing technologies make it ideal for precision devices, medical precision parts, and precision screws, as well as mechanical watches.


  • Precision springs (coils, torsion springs, flat springs, disc springs)
  • Springs for measuring instruments
  • Cable guides for driving robot devices
  • Medical precision parts
  • Wires for medical devices


Tensile strength ~ 2156MPa (~ 220kg/mm2)
Elongation 3.00%
Hardness Hv.~ 600
Density 8.3 ~ 8.6g/cm3
Young’s modulus 206 ~ 216GPa (21 ~ 22X103kg/mm2)
Modulus of rigidity 80.4GPa (8.2X103kg/mm2)
Linear expansion coefficient 12 ~ 13X10-6/°C (20 ~ 50°C)
Electrical resistivity 98 ~ 100µΩ-cm

(Wire drawriing material: cold processing + age treatment)