The Fence Trainer is the result of years of trial and effort. Made from high-impact plastics, this tennis training aid has features not found in any other training device, making it the most versatile swing trainer available. The tennis balls have an exclusive highly durable solid core. One of the balls is used for groundstrokes and volleys, and the other for serving. And, best of all, the height of each ball is completely adjustable to the desired swing height of each player. Shipped in 3 pieces, the Fence Trainer assembles and sets up securely on any fence in seconds. No ladder or tools needed.