O-ring for the quartz sleeve holders — the fittings that locate and clamp the quartz sleeve, also called a quartz tube — on older Katadyn ultraviolet disinfection systems. It seals the holder against the sleeve, keeping the treated water out of the dry lamp compartment. A low-cost consumable that is worth stocking, because it is single-use and a sleeve cannot be refitted properly without it. Reference number 11100-0309.