The cast iron caster wheels provide high capacity and are less expensive than forged steel caster wheels. They are practical for use on wood block or hardened smooth concrete. On untreated concrete they tend to cause rapid floor deterioration. Although the treads are machined smooth to minimize floor wear, iron caster wheels are not recommended where floor or cargo protection is needed. Gray iron is a tough, long wearing material, but it does not have the impact strength of ductile or forged steel. These caster wheels withstand shock and impact in all but the most severe applications.