You get three (3) of these PTL18 filter elements that will fit your Vita Duet oval spa.  They can also be used for almost any spa that has a 1.5" female threaded opening.  Each is 8" tall not including the threaded nipple and 4.5" in diameter.  If you have three you can rotate the clean ones in each month and let the dirty ones soak overnight, rinse well, then let it dry.  The drying helps to shrink the fabric back to the original manufactured state and kills any remaining bacteria.  Good idea..... get 3!