(Bloomberg News) A New York Yankees baseball cap worn by Hall of Famer Babe Ruth has gone up for auction, 15 years after David Wells donned it for an inning on the mound at Yankee Stadium.

Worn by Ruth in the early 1930s, the navy blue flannel cap is worth an estimated $400,000, according to SCP Auctions, which is handling the sale. The auction opened yesterday and closes on May 19, the company said in an e-mailed statement.

Wells, 48, bought the hat for $35,000, according to the New York Times, and wore it in the first inning of a game he pitched on June 28, 1997, against the Cleveland Indians.

"Babe Ruth has always been my biggest idol," Wells said in the statement. "It has been an honor to be the caretaker of his Yankees cap for all these years. I'll never forget what a thrill it was to honor the Babe by bringing the cap back to Yankee Stadium and wearing it on the mound."

In a 22-year career spent with the Boston Red Sox, Yankees and Boston Braves, Ruth hit 714 home runs, third on the career list behind Barry Bonds and Hank Aaron. An outfielder and pitcher, Ruth led the American League in home runs 12 times and his 2,213 runs batted in are second only to Aaron.

The Ruth cap is identifiable to a period from 1930-33, according to the statement. It features the Yankees' interlocking "NY" logo, as well as "G. Ruth" embroidered on the interior leather band. Worn in an era before batting helmets, it is believed that Ruth -- whose full name was George Herman Ruth -- wore the cap both in the field and at the plate.

"This is a truly exceptional relic that captures the essence of the most prolific athlete in the history from the Golden Age of American sports," SCP Auctions President David Kohler said in the statement.

The last game-worn Ruth hat to be auctioned sold in 2008 for $327,750, Kohler told the New York Times.

The cap is part of a spring auction that includes a Ruth game-worn Yankees jersey estimated to be worth as much as $2 million, a game-used bat worth around $200,000 and a baseball signed by Ruth and Yankees Hall of Fame first baseman Lou Gehrig worth up to $45,000, according to the release. Also included in the auction is the hat that New York Giants outfielder Bobby Thomson wore when he hit the "Shot Heard Round the World," a season-ending home run against the crosstown Brooklyn Dodgers to win the 1951 National League pennant.