US Patent 7232186 Depth-adjustable device for a chair

A depth-adjustable device for a chair comprises a rail rack, the railway is formed with a V-shaped concave, and the supporting board is slideably disposed in the railway by four clipping blocks, and in the lower part of each clipping block is formed a V-shaped convex. The inclined concave cooperates with the inclined convex to allow the adjustment device operate firmly. The V-shaped convex of the clipping blocks moveably abuts against the V-shaped concave in the bottom of the respective railways of the rail base, so that the gravity will be focused on the center and the supporting board and the rail base will slide relative to each other but will not wobble and impact each other, thus reducing the operation noise effectively.