Casual viewers of Major League Baseball have probably noticed that players warming up sometimes take practice swings with a peculiar apparatus attached to their bat. It looks kind of like a ring, fixed to the mid-to-upper length of the bat, but it’s taken off prior to hitters stepping to the plate.

Is it a bat cozy, meant to keep bats warm? Is it a theft-deterrent device?

Neither. It’s a bat doughnut, and there’s a belief—though not hard evidence—it can help players with their hitting.

The idea is that batters who warm up with a heavier weighted bat and then swing a conventional (and lighter) stick will be primed to swing faster and hit harder because the bat feels (and is) lighter. The doughnuts, which can weigh as little as 4 ounces up to 28 ounces, easily slide on and off the bats. Some players also use special weighted bats, which have no accessories but can weigh up to 55.2 ounces, far more than a standard 31.5-ounce bat. Many players start using the doughnuts in Little League. (They currently prohibit doughnuts but allow weighted bat sleeves.) Some may even go old school and swing multiple bats at once to get a similar effect.

Manny Machado of the Baltimore Orioles uses a bat sleeve to warm up in 2016.Matt Brown/Angels Baseball LP/Getty Images

But it seems like tradition may be more of a motive than science. In 2011, researchers at California State University, Fullerton studied 19 volunteers who swung light, regular, and heavy bats before moving to the plate. Heavier bats didn’t improve their performance with a regular bat. In fact, it made them slower, moving bats at just 77.2 kilometers per hour compared to 83.7 kilometers after having used a light bat or 80.5 kilometers when using a standard bat for practice.

The history of the doughnut is a little murky. A construction worker in New Jersey named Frank Hamilton thought swinging multiple bats was silly, and so in 1967 he patented a weight attachment. Hamilton approached Elston Howard, the first Black player on the New York Yankees and who lived nearby, to endorse the product, which they dubbed Elston Howard’s On-Deck Bat Weight. Mickey Mantle and Willie Mays were among the players intrigued, and the doughnut became a dugout staple.

Whether it's actually effective may be beside the point. In baseball, nothing beats a good ritual.