Hayward C17502S Star-Clear Plus 175-Square-Foot Cartridge Filter, 2-Inch SKT Pipe Single piece injection-molded base and body provides added strength for reliable, corrosion-free performance Single locking knob securely fastens head to filter tank, eliminating bolts or clamps Attractive, durable filter head may be rotated to conveniently position pressure gauge and manual air relief Extra-large cartridge element with New precision engineered extruded core provides extra strength and maximum flow