Baseball/Softball On-Deck Circle Bat Weights (Available in 7 Colored Weights) PowerSwing Bat Weights by Markwort. Cast iron bat weights are color-coordinated according to their respective weight. Use for training and building arm strength. Use on Little League & Senior League Big Barrel Baseball and Softball Bats Used by players in practice and in games in the On-Deck Circle to get the bat to feel lighter, creating a quicker swing through the hitting zone.