This is a Pump Trap Lid O-Ring for Pentair WaterFall, WhisperFlo and IntelliFlo VS, I1, VS 3050 and VS + SVRS, Challenger High Pressure Pumps. Measurement is 5.85 x 0.275.
This o-ring is used with various pumps such as the Model AFP-75, AFP-120 and 150 Waterfall, WhisperFlo High Performance and IntelliFlo VS, I1, VS 3050 and VS + SVRS, Challenger High Pressure Pumps.