This round rubber mount, which sits at the top of your front strut assembly, features a precision bearing in the center that allows the strut to turn when the car is turned. If your front end is wobbly or making other strange noises or movements, jack the car up and check your strut bearings for wear or damage. If they are worn out, replace them, you will feel like you have got a new car!
If your strut bearings are worn, chances are your inserts are as well. Replace the whole assembly all at once with no special tools and save time and money. If you just want to replace the strut bearing, you will need a spring compressor like the one shown below.