new Diameter(.): Rubber:29mm/1 Plastic:31mm/1 Installation calls for tools: a screw driver or Wrench, a thick cloth. To remove your damaged piece, you should use a plier, a thick cloth, and mineral oil or any other oil for lubrication. Colour: black Material: plastic + metal Package Contents: 2 * Black transmission wheels four * Black translucent transmission wheels Only the above package content, different item should not included. Note: Light and diverse reveals can cause the color of the item within the photograph a little bit varied from the genuine thing. The size allowed error is +/- 1-3cm.