The excircle of  top compression ring and bush ring is plated，the second ring is nodular cast iron ：
● The excircle has a hardness of more than HV850
● The Chromium layer is a loose hole, which is different from ordinary，In the case of poor lubrication, it can increase the wear resistance of the plating layer
● It has high demands on the production
● Under normal conditions，It can use 1,5000KM