Item 15392 Mass Damper Set and Item 15401 Mass Damper Set (Heavy) are a standard modification used by Mini 4WD racers all over the world. These mass dampers are now available in new colors (Black & Silver) Specs and Features Weight x 2pcs. Ball Cap x 2pcs. 2x25mm or 2x30mm Screws x 3pcs. each. Spacers, washers, and nuts included.