The Culligan® OR-100 O-Ring is designed for use in the following heavy-duty whole house water filters with a 1-inch inlet/outlet: Culligan® model HD-950A. The o-ring is used to seal the housing canister to the housing cap to prevent leaks. Replace your o-ring with every third filter change or when there is damage to prevent leaks. Product Features O-ring is used to seal the housing canister to cap to prevent leaks in filter system Replace the o-ring with every third filter change to prevent leaks Use with Culligan® HD-950A Product Specifications Package includes: OR-100 Temperature Range Fahrenheit: 40 – 100°F Product Dimensions: 5.75 X 5.75 X .19 Use With: CW-F, CW-MF, P5, P1, S1A, SCWH-5