This rigid, medium-duty plate caster is made of zinc and can handle loads up to 300 pounds. The mounting plate is 4 1/8 x 3 1/8 inches, with inside and outside bolt hole spacing of 2 3/8 x 3 1/8 inches. The mounting bolt diameter is 3/8 inches. The wheel is 1 1/2 inches wide, four inches in diameter, and made of blue elastic with a black core. The replacement wheel number is WBZ4BB.