Composed of a horizontal plate, inclined plate, car, several rough degree of different materials, steel balls, and the slope of the transition plate; horizontal plate size 530 mm x 120 mm x 12mm; inclined panel size 200 x 12 x 12 mm, galvanized hinge for connecting inclined panel and the horizontal plate; abaxial surface with 3mm diameter galvanized support; car formed by injection molding, the bottom is provided with four galvanized wheels and two loading block; slope transition plate made of plastic injection and, size: 195mm * 120 mm x 4 mm; middle ball rolling groove, both sides of one end of the open gap.