The 2H hex nut is also known as the heavy hex nut—commonly used in heavy-duty applications. They have a larger size and higher strength than standard hex nuts. These help distribute the load over a larger surface and prevent damage to the surfaces the nut is tightened onto. Black iron hex nuts, in particular, have a black oxidized finish created during manufacturing. This finish helps protect the surface from corrosion. Black iron hex nuts are also typically stronger than their galvanized counterparts due to the higher carbon content in their steel.