This replacement ball for the Turnoverball Gooseneck Hitch is 2 and 5/16" and is machined for a tight, rattle-free fit. The "corners only" fit of the square ball base in the round portion of the socket allows dirt to fall through the socket, reducing the chance that the ball might seize up. Warning: This product can expose you to chemicals which is [are] known to the State of California to cause cancer and birth defects or other reproductive harm.