This vice is suitable for medium to heavy-duty applications and is made from Spheroidal Graphite (SG) cast iron, also known as SG iron, or Ductile Iron. During the manufacturing process the Graphite (carbon) element of the steel is shaped and aligned and adds the important 'spherical' aspect to the name. This makes these vices both virtually unbreakable as well as much lighter than conventional grey cast iron, the material traditionally used for the construction of mechanics vices.