Ideal for working out/exercising and for use in on deck circle. It increases bat speed and strengthens hitting muscles, and will dramatically improve performance and timing at the plate. Builds quickness, power and a proper swing. The fins provide resistance throughout the entire swing to attain maximum effect when the velocity is greatest. Recommended for workouts during team practice sessions. One size fits all baseball and softball bats, little league, high school and college. Assembly instructions included. Weighs 14 oz.