Piston ring:
1)High Quality
2)Full Range
3)Good Service
4)Excellent Package

Materials (_)
1)black cast iron ball
2)alloy cast iron
3)high-alloy cast iron
4)stainless: 6Cr 13Mo
72A
304

Performance():
1)good thermal stability
2)high bending strength
3)good stretch

Hardness():
1)basic hardness is HRB and HRC
2)Chromium and Nitride layer are HVO. 1