Many manufacturing industries use equipment that can move loads up to 40,000 and sometimes even 50,000 pounds. Especially heavy-duty bins and dollies need wheels that can carry such extreme loads. These wheels are called industrial casters and are specially designed and made. They usually have a forged iron core and a plastic or rubber tire. Rubber is used when the factory floor is moist, since it provides grip and reduces noise. Phenolic resin is another material that works well for industrial casters, because it prevents oily substances from attaching to the wheel surface. Heavy-duty wheels also have to absorb shock, when extremely heavy loads get dropped onto the equipment. Industrial casters often go unnoticed, but they are an interesting and challenging area of engineering.