Different baseball leagues allow specific types of bats which fall under various certifications based on their Bat Performance Factor (BPF). In short, BPF is the measurement of a bat’s liveliness.
BBCOR (0.50 BPF): BBCOR is the standard certification of adult bats used by high school and collegiate players. This certification allows a maximum barrel diameter of 2 5/8 inches.
USSSA (1.15 BPF): USSSA is the standard certification for travel baseball. This certification allows a maximum barrel diameter of 2 3/4 inches.
USABat USABat is the standard certification for youth baseball. The goal of USABat is to establish a wood-like performance for youth baseball bats. This certification allows a maximum barrel diameter of 2 5/8 inches.