The guide ring or wear ring guides a hydraulic cylinder piston and rod and absorbs lateral forces. Metal to metal contact between the moving parts of the cylinder, for instance between the piston and the cylinder or the rod and the cylinder head. The advantages of these non-metallic guide rings (compared with traditional metal guide rings) are, among others, a high bearing load capacity, the elimination of local stress concentrations, wear resistance, a low coefficient of friction, and low maintenance costs. http://www.kintoweseals.com/hydraulic-seals/guide-rings/