Pair of wheels for volcanic stone mill. Ideal for grinding nixtamal, corn, coffee, dried chili peppers, spices, beans, beans, wheat and cocoa. Made by artisans from San Salvador el Seco. These wheels are used as a replacement for nixtamal mills or for ornamental use. Bolt Measurement: -Center Bolt Diameter: 1.5 inches. -Small bolt diameter: 3/4 inches. Spacing between bolts from center: -First pair of bolts: 1/2 inch. -Second pair of bolts: 1/4 inch.