HSS 4" wheel casters are ideal for use in your home, office, business, restaurant, medical facility, residential facility, hotel, motel or other environments. It has a rubber and metal construction for a durability that will withstand daily use. It fits wire shelving poles with insert bolt size 3/8". Simply screw them into the bottom pole to install. Each set comes with 2 non-locking wheels and 2 locking wheels that keeps shelving unit in place. They have a maximum loading capacity of 600 lbs., making them suitable for placing under large units.