Before buying a new bat, you should read the entire rule, which can be found by clicking HERE. Here is a summary of the rule:
A bat must either: (1) be a single, solid piece of wood that meets the specs below or (2) any metal or composite bats must bear the "USA Baseball" logo and the barrel can be 2 5/8 inches or 2 1/4 inches. They are not allowed to be 2 3/4 inches.
For Tee Ball ONLY: New tee ball bats must bear the "USA Baseball" logo. Older tee ball bats are OK if they have an ELL sticker from a previous season, but they will need to get new stickers.
Wood bats: Must not be more than 33 inches in length. Must not be more than 2⅝ inches in diameter. Must not be not less than fifteen-sixteenths (15/16) of an inch in diameter (or 7/8 inch for bats less than 30 inches) at its smallest part. Grips (taped or fitted sleeve) cannot extend more than sixteen (16) inches from the small end. Note: Solid one-piece wood bats do NOT require the USA Baseball logo.