These Ag cutting discs are the new Inphinium steel. They are 55 Rockwell through and through, and the better answer to the French Forges de Niaux 200. They are 18 and 18 5/8" inch (actual size is about 18.2" and 18.675"). These are for John Deere Pro Series, 95, 90, 60, and 50 series drills and air seeders. I also have Standard Ingersoll discs at 18 inch made from their common steel. $45 for Inphinium 18", $49 for Inphinium 18 5/8", $35 for standard 18" Ingersoll.