KJ T-SPRING XR6 - GRAY (PAIR) – Adjustable/Interchangeable Tension Bands to fit your weight of usage. This is replacement T-Spring for KJ-XR3 series. It is also compatible with KJ-Pro7 series (as a softer T-Spring option), as well as older KJ-XR series. This T-Spring model features: the new 4 Twin Turbo System (for improved balance & rebound), and the new SRS (Safety Release System). It is "Coil Spring Adapted", which means that you can attach the optional steel Coil Spring to customize the compression resistance of your KJ Rebound Shoes.