Quoted directly from the 2019 PONY Baseball Rulebook
C. Wooden, metal, graphite or ceramic bats manufactured for baseball play, which are round and not more than two and five eighths inches in diameter at the thickest part, not more than 42 inches in length, are acceptable. No bat shall be used if dented, cracked, modified or misshaped. The bat’s knob may be solid or hollowed to house an embedded metric sensor. If a sensor is used, it shall (1) not affect performance; (2) be secured by a locking mechanism and a back-up mechanism to keep it in place; and (3) have a distinguishing “off-line” mode to prevent data from being accessed during a game.
(1) Bats manufactured specifically for use in tee ball, shall not be used when the ball is pitched by a player, coach, or pitching machine, unless using a safety ball. Coach-pitch bats will only be used in coach-pitch using a safety ball. Penalty: removal of the bat only. (Not subject to rule 18-E-7(a), (b) and (c). If using a tee ball bat manufactured prior to 2018, these bat must carry the USA Baseball mark accompanied by the following text: “Only For Use With Approved Tee Ball Bat.” If you already have a tee ball bat you would like to continue using, all you have to do is purchase a USA Bat sticker directly from USABB and place it on your bat.
(2) In conjunction with USA Baseball and its other participating national member organizations, PONY Baseball has adopted the new USA Baseball bat standard (USABat). Effective January 1, 2018, with the exception of the -3 bat (BBCOR certified), all other 2-⅝ inch minus factor bats (-5, -7, -9, etc.) and 2-¼” bats must be certified with the USABat licensing stamp on the bat in order to be used for league and tournament play. 2-¼″ BARREL bats are legal in all divisions of PONY Baseball except COLT 16U™, PALOMINO 18U™ and THOROBRED 23U™. 2-¼” and 2-⅝ inch minus factor bats (-5, -7, -9, etc.) used in 2017 will be illegal to use in 2018.
(3) 2-⅝” barrel bats are legal in all division of PONY Baseball. If a 2-⅝” bat is -3, it must be BBCOR certified (stamped on the bats). Effective January 1, 2018, all other minus factor bats (-5, -7, -9, etc.) Must be certified with USABat licensing mark stamped on the bat.
(4) 2-¾” barrel bats are prohibited in all divisions of PONY Baseball.
(5) COLT 16U™ and PALOMINO 18U™ are only allowed to use 2-⅝″ -3 BBCOR certified bats.
(6) THOROBRED 23U™ League must use wooden bats only as specified by Major League Baseball.