High end practice golf balls, 42mm diameter, 6 grams.

This is one of the keys to why the MaxBP is such a great tool. These mini (golf ball size) training balls are much smaller than anything you'll have to hit in a game. So by the time you reach competition, your brain, your nervous system, and your body are already conditioned to handle a hitting task much more difficult than the one in front of you on game day. The MaxBP can hold over 100 balls, so to get the most of your batting practice time, it's a good idea to get at least that many balls. And maybe a few more, you'll probably end up hitting a few onto the roof!