My dog loves fetch and I am a huge fan of the Chuckit! launcher, however the tennis balls only seemed to last about a week tops.  The felt disintegrates and then the rubber ball splits into two pieces.  I thought this was just how life was going to be: forever buying these balls for our launcher.  Then a friend told me that they just use regular tennis balls so I tried it.  I bought a pack of 10 cheap-o tennis balls for the same price as I was paying for 2 Chuck it balls and three weeks later we're still using on our first ball- amazing!  It fits perfectly in the launcher and still has felt and bounce.  Thank you, Chuckit! for making the medium sized launcher a standard tennis ball size.  I will happily buy another launcher if my current one ever wears out, but I won't waste my money on these tennis balls.