Transport delicate parts and materials virtually on air. Shock absorbing, full pneumatic tired, roller bearing wheel absorbs vibrations which could be harmful to load, while protecting floors. Corrosion-resistant electroplated casters provide years of dependable service. Gray rubber tires. Features slotted bolt holes that help align screws to mounting surface. 4-1/2 x 4 plate size. 2-5/8 to 3 x 3 to 3-5/8 bolt spacing.