The purpose of explosion-proof hex keys: They are specifically designed for tightening or removing round nuts on machine tools, vehicles, and mechanical equipment. After being shaped, the explosion-proof hex keys undergo a high-temperature bluing process, where they are immersed in a solution with a high content of sodium hydroxide and sodium nitrite at a temperature above 140 degrees Celsius. This process results in the formation of a dense oxide film (Fe2O3 and ...) on the surface of the steel parts.