In foundry application, the medium grades: #49, #56, #63 offer high permeability due to excellent fines control and are ideal for most core and molding applications in iron, steel and non-ferrous foundries. They also offer high strength in all binder systems.
 

The finer grades: F 71 consist of rounded to sub-angular grains, which provide high strength and excellent permeability. They achieve superior casting finishes in all binder systems and metals.