The Hydronix HF45-20CLBK15 Big Blue size 20" Clear Filter Housing is an extra-wide housing that accommodates large 4.5" wide filters for increased flow. It is made of a durable Polycarbonate that is usable with a variety of none corrosive chemicals. The housing cap is a high-flow polypropylene cap with 1/2" external female NPT ports and large internal ports, allowing water to pass through rapidly. This Hydronix Big Blue size filters is an excellent choice for whole house or commercial applications where high flow rates are required.