Carrier Roller guides the track chain on the upper side of the undercarriage to keep it in line. We mount it above the track frame so the chain does not sag or slip off when the machine moves. It rolls on a smooth shaft, reducing friction. Made from hardened steel, it stands up to dust and bumps. When it wears out, we swap it to keep work going. Think of it as the chain guide on your bike keeping the belt tight. No wobble.