Uxcell a11040200ux0061 Chair Twin-wheel Black Caster with Threaded Stem Connector Material: Plastic, Metal Stem Thread Size: 0.78 x 1.5cm / 0.3" x 0.59" ( D * H) Wheel Diameter: 4cm / 1.5" Total Size (Approx.): 4.7 x 6.5cm / 1.8" x 2.5"(D*H) Color: Black