By heat-treating our steel 22, 28, 32, and 38T chainrings they have gained a 200% increase in yield strength over typical steel rings. This new heat-treatment makes our inner and middle cromoly chainrings nearly as hard as a cogset. Perfect for wet and muddy climates, or for those of you who go through alloy rings quickly. Also available in 28-38T combo to be used with 28-38-Rockguard chainring combinations (for example, our Holzfeller crankset). Backwards compatible with our 2000 series chainrings. Use with 9-speed chains. 4-bolt pattern.