Feature●Replacement Ball and String for Tennis Trainers●Long elastic cord brings the ball back so you can hit it again and again●Great for practice and grooving your strokes●Made for the Tourna Fill-n-Drill Tennis Trainer but can be used on any water filled tennis trainer●Fits all tennis trainersDescription Fits all tennis trainers with a water filled base. Simply tie around the base with a secure knot and youre ready to play.