The very best dykes rings ever made for karting were from Hartman Engineering (the rings were actually made by Pacific Piston Ring in Los Angeles). This is from the era when dykes rings were standard on the Assos-made pistons we ran back then in the Italian engines.
The Hartman rings were made from 17-4 stainless, and hard-chrome plated and ground. They had very little tension... VERY little. The rings were so good you could run one for a season... just change pistons. (all engines were cast iron bore, no Nikasil back then).
I probably still have one in the cabinet somewhere... I'll take a photo and will post.
Pete