This set includes 12 pieces of hollow golf training balls, each with a diameter of 42mm, matching standard golf ball size. Made of durable plastic, they feature an airflow design that limits flight distance, making them perfect for swing practice in limited spaces. These balls are ideal for indoor swing training, driving range practice, and home backyard use. They help golfers improve swing posture and strength without the risk of flying balls hitting surrounding objects, suitable for both beginner golfers to practice and experienced players to warm up before formal games.