Tungsten Carbide 8 mm (5/16 in) Comfort Fit Flat Wedding Band Ring w/ Brushed Center & Beveled Edge (Available in Sizes 8 to 11) 8 mm (5/16 in) Comfort Fit Flat Wedding Band Ring with Brushed Center & Beveled Edge. Completely cobalt-free and ranks next to Diamonds as the 2nd hardest material in the world. Flawlessly shaped pure Tungsten Carbide. 100% Satisfaction Guaranteed.