Flame hardening processes are applied to individual parts in a manner to achieve distinct areas of differing hardness and toughness.  The treatment is typically used on wheels, to harden the rolling surface; gears, to harden the teeth; shafts, to harden bearing journals, and levers, to harden the wear end.  Flame hardening is usually done by hand on small lots, or on automated equipment for high production quantities.  Parts made of materials with insufficient hardenability can be carburized first to produce a hardenable surface and then flame hardened in the specified area.  Large parts can sometimes be progressive hardened over long lengths or large diameters.