This is a set of 4 jack pads for Model 3, Y, S, and X.
These are used whenever you need to jack up your car.
They are typically used for seasonal tire changes, tire rotations, etc.
Place them into the designated jack points (see your car manual for details) and then you can jack the car up without damaging the rocker panels or battery.
There is a set of 4 which can be used when you use a vehicle lift, although you may need only one if you are using a floor jack.