POLYURETHANE TREAD: Heavy duty caster is made of a thickened polyurethane tread for long life and keep all floors clean and free of tread marks. The crowned tread, combined with high-quality Polyurethane provides both shock absorption and resilience, ensuring a quick momentum build-up and offering the industry's top ergonomic ride. ALUMINUM WHEEL CORE: Aluminum wheel cores are lighter in weight than cast iron wheel cores and will not rust. Because of the unique wheel tread, the caster wheel can deflect debris to help keep the wheel clean and decrease maintenance costs. HEAVY DUTY LOAD: Industrial casters designed with strength and sturdiness in mind, ensuring a long lifespan and easy movement of large, heavy loads. Each caster holds a maximum of 800 lbs.(Sets of 4 load 3200lbs) WIDE APPLICATION: With polyurethane on aluminum wheels offer abrasion resistance, oil, and chemical resistance and are non-marking helping you protect your floors. 4 inch casters are suitable for indoor and outdoor. Heavy duty wheels are very popular in applications such as warehouses, and automotive facilities,Research Laboratories, Hospitals, Bakeries and many Industrial Manufacturing facilities.Maintenance-free caster wheels heavy duty. SOLID & SMOOTH: Outdoor caster wheels design with industrial-strength precision ball bearings, these ergonomic wheels guarantee durability, longevity, and superior roll-ability. Mark-free gliding experience on a variety of floors. NINOSO 4" Casters, Heavy Duty Industrial Caster Wheels, Aluminum Core Thickened Polyurethane Casters Set of 4 with Load 3200lbs Capacity, Wheels for Cart Toolbox (2 Brake & 2 Swivel)