The weights shall be corrosion resistant. The quality of the material shall be such that the change in the mass of the weights shall be negligible in relation to the maximum errors permitted in their accuracy class under normal conditions of use and the purpose for which they are being used.

1. Class E1 and E2 weights:- For weights equal to or greater than 1 g, the hardness of this material and its resistance to wear shall be similar to or better than that of austenitic stainless steel.

2. Class F weights:- The surface of class F weights greater than or equal to 1 g may be treated with a suitable metallic coating in order to improve their corrosion resistance and hardness.

• For class F weights greater than or equal to 1 g, the hardness and brittleness of the materials used shall be at least equal to that of drawn brass.
• For class F weights greater than or equal to 50 kg, the hardness and brittleness of the materials used for the whole body or for the external surfaces shall be at least equal to that of stainless steel.

3. Class M1, M2 and M3 weights of 50 kg or less:- The surface of weights equal to or greater than 1 g may be treated with a suitable coating in order to improve their corrosion resistance or hardness.

• Class M weights less than 1 g shall be made of material that is sufficiently resistant to corrosion and oxidization.
• Cylindrical class M1 weights below 5 kg and class M2 and M3 weights below 100 g shall be made of brass or a material whose hardness and resistance to corrosion is similar or better than that of brass. Other cylindrical class M1, M2 and M3 weights of 50 kg or less shall be made of grey cast iron or of another material whose brittleness and resistance to corrosion is similar or better than that of grey cast iron.
• Weights with a rectangular parallelepiped shape from 5 kg to 50 kg shall be made of a material that has a resistance to corrosion that is at least equal to that of grey cast iron. Its brittleness shall not exceed that of grey cast iron.
• The handles of rectangular parallelepiped weights shall be made of seamless steel tube or shall be cast iron, integral with the body of the weight.

4. Class M weights greater than 50 kg

• The surface of the weights may be treated with a suitable coating in order to improve their corrosion resistance. This coating shall withstand shocks and outdoor weather conditions.
• The weights shall be made of one or more materials that have a resistance to corrosion equal to or better than that of grey cast iron.
• The material shall be of such hardness and strength that it withstands the loads and shocks that will occur under normal conditions of use.
• The handles of rectangular parallelepiped weights shall be made of seamless steel tube or shall be cast iron, integral with the body of the weight.