Secondly, why do people hang tennis balls in garages?
Hanging a tennis ball on a string in your garage helps you to easily determine where to stop and conversely know your car is far enough inside for your garage door to close.
Besides, how do you get a string through a tennis ball?
Garage Parking Gauge
Punch or drill a hole through a tennis ball, run a piece of string through the hole, and tie a knot below the tennis ball. Thread the string through both eye hooks and attach it to the open garage door so the tennis ball is level with the front of the car when the garage door is open.
How do you stop a garage parking?