A4 stainless steel A4 steels, alloyed with molybdenum, are "acid resistant" and provide better corrosion resistance. A4 is used extensively in the cellulose industry, since this grade of steel was developed for boiling sulphuric acid. It is also suitable to some extent for chloride environments. A4 is also frequently used by the food and shipbuilding industries. Heavy Duty Flooring "Heavy Duty" means that the floor/panel is suitable for heavy loads (please contact us to find out the maximum loads for the floor/panel you require). The floor lift can be operated manually and is usually fitted with safety locking systems to keep the floor in place when it is raised. It is important to choose a là¨ve-plancher that is suitable for the size and weight of the floor, as well as the boat's spà©cifications.