The disc is a replacement part made by Zodiac for the TR2D suction side cleaner. It is made from the same high-grade rubber material as the original factory part.
The disc sweeps up dirt and algae off the surface of the pool kind of like a broom does on the surface of your home (minus the algae). This also moves the debris and dirt towards the center of the cleaner to be sucked up, out, and into your filtration system.
The front disc is Silver with pronged like teeth that run along its edge. This provides greater maneuverability for the cleaner. It also creates better suction to pull up a larger range of debris and mulch off the surface of the pool.