Lifegard Aquatics QL UV Water Sterilizer, 15 Watts Solid cap features Clear View Port to allow visible light (no UV) to pass through and indicate bulb is operating The replaceable Internal Overflow Pipe automatically vents air from chamber and directs 100-percent of the water flow past UV light The Splash Boot creates water resistant seal around electrical connection Its unique 4-pin connectordesign allows easy bulb replacement without shutting down the system; All Lifegard Mechanical, Chemical, Heater, and UV Sterilizers include 3/4-inch threaded reducing bushings if threaded installation is desired