Elasti-Stroke Two Ball System is a great tennis training aid that improves tennis skills with a self rebounding ball. The self rebounding ball attaches easily to any racquet. The ready to play system features a 65 MM stage 2 low compression transition ball that is attached to an elastic cord and vibration dampener. The Elasti-Stroke Two Ball System also comes with 75 mm stage 3 ultra low compression ball and an extra ball attachment discs that can be used with any tennis ball. With the Elasti-Stroke One Ball System there are no balls to chase and no courts needed. It can be played anywhere.