is accepted is also pretty important. most automatic fetch machines are specifically designed for a certain type of ball. in fact, some of them go so far as to include the balls that should go with the machine and make it difficult to use with other balls, even if they are the same size. but you want to have a machine that takes multiple types of balls. the first reason is that even if balls come with the machine, there is a possibility that they can get lost or destroyed, and you want to be able to provide your own balls instead of spending what is likely a great deal 