A suspension strut bumper, or bump stop, is a compressible suspension component designed to prevent metal on metal contact as the suspension undergoes extreme compression, like hitting a bump or pothole. Bump stops usually sit over a shock or strut shaft but may also be used externally to the shock or strut. They’re usually made of rubber or polyurethane. If you find your car bottoming out more than it used to, it might be time to replace your strut assembly, and inspect the strut bumpers for damage.