Aquadynamic design of screens holds the cake out of water for long life. Cage holds surfactants and odor counteractant until released by valve. Safe to use. . . Contains no paradichlorobenzene to contaminate water. Banned in more and more areas because they contaminate ground water, "para" toilet bowl and urinal blocks have been difficult to replace. Until now, producers have merely placed non-para cakes in old fashioned screens and holders; it hasn't worked. The non-para cakes dissolved too quickly and their deodorizer content was going down the drain instead of into the air. Now RX 110 urinal screens and RX 120 toilet rim cages house new, reformulated, longer lasting blocks with more AIRICIDE true odor counteractant plus enzymes. Of equal importance are the cages or holders. They are aquadynamically designed especially for our unique non-para cakes, to channel less water across the cake and continuously release more odor counteractant into the air.