An alternative to using batting donuts, the Markwort® Power Fins Hitting Trainer allow you to work against air resistance with each swing to help build strength, increase hand and bat speed, and develop stronger wrists. Train With Purpose: Unique design works against air resistance with each swing to increase strength and speed Operates similarly to batting donuts without the potential harm associated with them One size fits all baseball and softball bats Assembly instructions included Weight: 14 oz.