Bottom Roller 6814890 for Bobcat models 337 341 435 Bottom Roller 6814890 for Bobcat models 337 341 435 Bottom Roller. Track rollers, also known as lower or bottom rollers, are designed to transfer most of the machine's weight and dynamic forces to the ground through the tracks. Forged from deep hardened steel, they are heat treated to increase internal strength to resist bell-mounting and improve rebuildability. Heat-treated housings increase body strength and extend service