Babe Ruth's 104-year-old, one of a kind, game used, high school baseball mitt is about to hit the auction block ... and is expected to fetch close to $1 MILLION ... TMZ Sports has learned.
The catcher's mitt dates back to 1912 ... when Ruth attended St. Mary's Industrial School for Boys in Baltimore and played on the baseball team. He later gave the glove to a kid -- and the family held onto it for decades.
The mitt's been on display at the Babe Ruth Museum since 1993 -- but now the family has decided the time is right to sell .