Subaru 2005 Impreza Owner's Manual page 333

Driving tips
2. Insert the hitch pin into the hole on the hitch receiv-
er tube so that the pin passes through the ball mount.
8-26
UG8032BA
3. Insert the safety pin securely into the hitch pin.
4. Pull the ball mount to make sure it does not come
off the hitch receiver.
HS8012BA