UPDATED 2019 OPBA BAT RULE:

Baseball:

Bat Rule is as follows:
Tball through BJPW - Barrel size no bigger than 2-1/4" - USA and USSSA with 1.15bpf stamp allowed
PeeWee and Midget - Any USA bat with barrel size up to 2-5/8" and any USSSA bat with 1.15bpf stamp up to 2-1/4" barrel size
Pony - Any USA bat with barrel size up to 2-5/8" and any bat with a BBCOR stamp.
Any drop can be used.

Girls Softball:

All Fastpitch softball bats must have a 2 1/4 inch barrel diameter and must not be over 34 inches in length and 31 1/2 oz in weight.

ASA

Bats must be marked with the ASA Certified 2004 stamp. These Fastpitch bats should perform within the limits of the 98 mph batted ball speed standard. Bats can be made from aluminum or other metals; fiberglass, graphite or other composite material; or wood. Bats can be made from one or multiple pieces.