The WH-PREFILTER-KIT-1-2025-ORING is a replacement O-ring designed for Tier1 whole house filtration systems utilizing a 20 x 2.5-inch cartridge prefilter housing. The O-ring measures 1/8-inch cross-section width with a 3-3/4-inch inner diameter and 4-inch outer diameter. Prior to installation, apply a food-grade lubricant to the O-ring to ensure proper seating and a leak-free seal. Do not overtorque the filter sump during reassembly, as excessive force can deform or compromise the O-ring. Following installation, inspect all mating surfaces for signs of weeping or leakage before returning the system to service. Replace the WH-PREFILTER-KIT-1-2025-ORING at every second or third cartridge change interval, or immediately upon any visible cracking or deformation of the existing O-ring.