C24R - Concrete. Silicon carbide grain. General purpose cutting, hard bond for long life. Masonry, concrete, stone. Cast iron and other ferrous metals. Specifications: Max RPM - 6600, 5/8-11 Super-Lock hub. Tech Info: Special silicon carbide grain formula is excellent for grinding masonry, concrete, stone and aggregate. All sizes reinforced with the highest quality fiberglass for maximum safety and performance. Super-Lock Hub on all 5/8-11 threaded wheels is the safest, vibration-free design.