Bullet Stroke device sizes, weights and lengths are individual and must be chosen individually. The better way is to start with a small device size, length and weight. A big device size is much heavier than a small one. A lack of technique and athletic skills can lead to injury, more with a big device size. It is better practice more time and by right technique with a small device size, than less time and lack of technique with a big one. Compare an actual tennis racquet size with Tennis Bullet sizes. A big device size (Red Color), can be compared to 4-3/8 tennis racquet size, a small (Blue Color) one to 4-1/4.