The GE WS03X10039 is the correct replacement O-ring for the following:
The GE Smartwater Filter O-ring WS03X10039, 151122 fits the FXHSC and FXHTC water filter cartridges and the GXWH30C and GXWH35F water filtration systems, and is also compatible with GE SmartWater Heavy Duty water filter housings. This replacement O-ring features a 5 9/16 inch inside diameter and a 5 7/8 inch outside diameter. This GE O-ring seals the water filter housing cap to the housing sump in order to prevent leaks.
GE Smartwater Filter O-ring WS03X10039, 151122 specifications: