This O-ring is used for Big Blue/Heavy Duty Housings by Culligan; Ametek; Pentek; US Filter; Plymouth; Kleen Plus; and American Plumber.O-ring is 5 3/4" in diameter and can be used in place of the OR-100 by Culligan. Buna-N FDA grade o-ring.This O-Ring is used in all Big Blue housings by Pentek with 1" and 1 1/2" Inner / Outer Diameters; EXCEPT the Big Clear Housing.This O-Ring replaces the W10-OR.An O-Ring is very important part of your water filter system, and it should be maintained and replaced regularly. The O-Ring serves as a gasketto sealthe housing sump to the housing cap to prevent leaks.Important O-Ring Tips:Inspect O-Ring during each filter change for damage, cracks, splitsCover O-Ring with silicon lubricant during each filter changeDo not overtighten filter sump (do not use filter wrench to tighten sump - only use wrench to loosen sump)Repace O-Ring every two filter changesThis is a sale for one(1) o-ring for 10 inch or 20 inch big blue housingPayment Methods:PayPal (Preferred) Shipping Details: Please pay with PayPal for fastest delivery. Personal checks may be held until cleared. All items ship via FEDEX GROUND /USPS/UPS GROUND within 3 business day of receiving payment, however we are not responsible for transit time and delays. Continental U.S. buyers pay shipping price listed. Alaska, Hawaii, and A.P.O. addresses, please contact us for a shipping quote and availability before looking. *Shipping & Handling is NOT just postage. It includes the time, effort & materials associated with the preparation & arrangement of shipment. We do not inflate shipping rates, however in order to save you money we will gladly combine shipping on orders with more than one item whenever possible. eCRATER checkout automatically combines the shipping charges. Please contact us with any questions.