This is the Hot Racing Progressive Shock Spring Set  for the Traxxas X-Maxx Monster Truck.                                                                                                        FEATURES: Soft at the beginning of compression to absorb small bumps, then                        becomes stiffer to resist bottoming on jumps and other big hits                       Provides additional tuning options for best suspension performance in                   any environment                                                                      Spring steel construction                                                                                                                             INCLUDES: Two Black Extra Hard springs                                                            Two Blue Hard Springs                                                                   Two Red Medium Springs                                                                                                                                SPECS:    Length: 6.29" (160mm)                                                                Inner Diameter: 1.13" (28.8mm)                                                       Outer Diameter: 1.29" (33.0mm)