They are what protects the top of the strut when you bottom out. When the front of the car bounces and the strut compresses, the small piece of foam(or bumpstop) stops the top of the strut from smashing the bottom and damaging the strut. It looks like a small piece of foam with 3 levels. One a little bigger than the other. Just cut one level off from the front. This allows a little more travel for the lowered suspension.