Please note Emperor Aquatics Ultraviolet Lights come in both 3" diameter housing (for maximum UV performance), and a 2" diameter housing (for reduced initial cost). Both are great products and even use many of the same "Replacement Parts". The 3" diameter body provides a much higher degree of performance - known as the SmartUV Series. The 2" diameter body - known as the SmartUV-Lite Series. Please note which Ultraviolet Light and or Replacement Parts you are looking for. Please be sure sure you are ordering what you want - please call us if you have questions. Questions? Comments? koilagoon@gmail.com Or give us a call 9am - 5pm MST (970) 484 - 9162