The Pentek 163516 quartz sleeve o-rings only need to be replaced if they wear out. The Pentek 163516 quartz sleeve o-rings are also used in the Ametek, American Plumber, and USFilter UV-110 and UV-120 Ultraviolet Water Filtration Systems. Pentek 163516 Quartz Sleeve O-Ring Kit is used for the Pentek UV-110-1, UV-110-2, UV-120-1, and UV-120-2 Ultraviolet Water Filtration Systems. New quartz sleeve o-rings are supplied with each Pentek 163509 quartz sleeve for the UV-110 system and the Pentek 163513 quartz sleeve for the UV-120 system. If you are buying a replacement quartz sleeve, you do not need to buy the replacement quartz sleeve o-rings.