The Pentek 163538 quartz sleeve o-rings only need to be replaced if they wear out. Pentek 163538 Quartz Sleeve O-Ring Kit is used for the Pentek UVS-110-1 and UVS-110-2 Slim-Line Ultraviolet Water Filtration Systems. Also used in the Ametek, American Plumber, and USFilter UVS-110 Ultraviolet Water Filtration Systems. New quartz sleeve o-rings are supplied with each new Pentek 163504 quartz sleeve. If you are buying a replacement quartz sleeve, you do not need to buy the replacement quartz sleeve o-rings.