What material must commercial weights greater than 6 grams be made of?

Commercial weights greater than 6 grams are required to be made of metal not softer than brass due to the need for durability and resistance to wear. Weights used in commercial applications must maintain their accuracy over time, and softer materials would wear down or deform, leading to inaccurate measurements. Metal, specifically brass or harder variations, provides the strength and longevity needed to withstand frequent handling and usage without significant degradation. This is crucial in maintaining the integrity of measurements in commercial transactions where precision is key.

Other materials such as plastic, glass, or ceramic might not offer the necessary durability or reliability for weights used in this capacity, making metal the preferred and mandated choice for weights exceeding 6 grams.