Dynamic Series Filter Lock Ring made by Pentair R172214 The Locking Ring is used on the following items: Dynamic Series V DSC 75, DSC 100 TOP LOAD IN LINE CARTRIDGE FILTER Dynamic Series II & III RTL/RCF TOP LOAD IN LINE CARTRIDGE FILTERMODEL RTL/RCF 1-1/2 IN. & 2 IN. HIGH FLOW Dynamic Series I DYNAMIC SERIES 1 INLINE CARTRIDGE FILTER MODELS: RDC-25 & RDC-25S, RDC-50 & RDC-50S Rainbow Automatic Feeders HIGH CAPACITY AUTOMATIC FEEDERS MODELS HC-3315, HC-3330, HC-3340 Predator II Mini-Cellular Media Filter Leaf Trap MODEL 179/179C