A pin and clip is used to secure the ball mount to the hitch. The pin comes in two sizes. A ½" pin is used for Class I & II hitches, while the 5/8" pin is used for Class III and larger
A lock can be used instead of a pin & clip. There is a variety of locks available to choose from. These also come in two sizes similar to pin and clips (1/2" & 5/8").