Replacement O-Ring (Culligan® # 00308465 ) is approximately 2-1/8" OD and used with Culligan® filter System 101 / 201 / 301 as well as the AC & H Series Reverse Osmosis Systems AC-15, AC-30, AC-50, LC-50 Aqua-Cleer Reverse Osmosis Systems and the Good Water Machine H-5, H-30, H-30S-R, H-30PRV-C, H-52, H-53, H-8, H-82, H-83, H-83SR, H-84 Reverse Osmosis Systems.