Abstract: A coupler for a ball type hitch has a body member that includes a socket portion and a closure mechanism that is slidably mounted on the body member for movement between the open position, a closed position, and a third overshoot position. The closure mechanism includes a lower retaining plate and a latch plate which automatically latches when the closure mechanism achieves the closed position. A spring biases the closure mechanism from the open position to the closed position and third position. The closure mechanism is retained in the closed position when the coupler is engaged to a properly sized hitch ball. The closure mechanism is free to move to the third overshoot position when the coupler is engaged to an undersized ball. Visual indicators exit the coupler body member when the closure mechanism is in the open or third overshoot positions. The retainer plate includes a lock receiving aperture for receiving a lock that prevents unauthorized opening of the coupler.