This medium-duty, rigid plate caster is 4 1/8 x 3 1/8 inches, load-rated to 250 pounds, and made of zinc. The mounting bolt diameter is 5/16 inches and the inside and outside bolt hole spacing is 2 3/8 x 3 1/8 inches. The grey, poly-loc wheel is 1 1/4 in width, four inches in diameter, and can be replaced using order number WPP4BG.