PISTON RINGS. ProX piston rings are made by OEM factories to exact specifications. ProX uses well known brands like Rikken Japan, TP and NPR to be sure you will get the quality you might expect from our brand. All ProX piston rings can be used in cast iron bores, nickel ceramic platings (Nikasil), boron composite and electrofusion bores. If the application has a OEM cylinder with chrome bores, ProX supplies a different piston ring as in the ProX piston kit.