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 in the food and shipbuilding industries. PIRAMID hinge Piramid Hinges are special hinges used for boat ports. Ports are openings in the sides of a ship for ventilation and cabin lighting. Piramid Hinges are used to fix the hatch cover to the ship's hull so that it can be easily opened or closed. Piramid hinges are usually made of brass or stainless steel to resist corrosion from seawater. They are designed with a mechanism that locks the scuttle in the closed position to prevent it from opening accidentally while sailing. Piramid hinges are also designed to be easily dismantled if necessary, to facilitate maintenance or replacement of the ports. Below is a table of technical dimensions: A x B C D x E F x B 70 x 30 10 30 x 23 100 x 30