PowerFins™ work against air resistance. Build swing strength, increase hand/bat speed, develop stronger wrists. Batting donuts have been found to more harm than good, as they upset your natural swing process & the weight distrubution of the bat. Swing mechanics are not altered with Power Fins. One size fits 2 1/4” barrel or larger barrels. Works on baseball/softball/youth league, high school & college bats. Weighs 14oz.