Tennis Stroke Extender designed to establish and control a stroke extension through a target, pass line and direction. Vertical extensions positioned in a straight line, 4 inch (10.2 cm) apart. Device flexible extensions made from a foam material, very easy to cut with a knife for height adjustments. A whole device length is 14 inch (35.6 cm). Recommended height is 20-26 inch (50-66 cm). There are two lengths of flexible extensions – regular (27.5 inch, 69.8 cm) and long (57 inch, 144.7 cm). Flexible extensions will be not damaged if they are mistakenly hitted by Tennis Bullet. Blue flexible extension on the video above is the target and impact sound must be exactly above. “Target” flexible extension can be positioned first, second or third in the row.