A 20kg weight refers to a physical measuring tool with a given mass and specified shape. Used for calibrating scales and measuring on scales. The combination of weights and scales (weights used on scales are often referred to as weights) is necessary to determine the mass of other objects, making it a subordinate physical measuring tool. Cast iron weights are composed of iron, carbon, and silicon, and have poor corrosion resistance. Therefore, many manufacturers will make appropriate treatments on the surface of the weights, such as chrome plating, oil coating, painting, and blueing, to avoid rusting. Among them, chrome plated weights are more common, and the chromium coating has good chemical stability and does not work in alkali, sulfide, nitric acid, and most organic acids.