Solid cast iron with a 2-inch center hole that fits any Olympic bar with a diameter of 2" or less; also works with 2" dumbbell bars. All plates have a long-lasting black baked enamel finish that resists rust and corrosion while emitting no odor. Each plate has three big apertures with gripping strips. For simple identification, the labels are labeled in both LB and KG. Weight plates can be used to strengthen muscles and develop endurance, as well as to improve flexibility and balance.