Get your leaking RO filter housings back in working order with Captain O-Ring’s replacement o-ring set. Includes four (4) o-rings so you can keep your system in top shape. Compatible with APEC Ultimate and Essence Reverse Osmosis Drinking Water Systems. Compatible with APEC Reverse Osmosis Filter Housing Models: RO-45, RO-90, RO-PERM, RO-PUMP, ROES-50, ROES-PH75, ROES-UV75, ROES-UV75-55 and ROES-PHUV75. This o-ring is available in two versions to cover different dates of these models: Version A (P/N: O-RING-SET) is compatible with APEC ESSENCE RO units made before June, 2013 and ULTIMATE RO units made before May 2015. Version B (P/N: O-RING-SET-B) is compatible with APEC ESSENCE RO units made after June, 2013 and ULTIMATE RO units made after May 2015. O-Rings measure approximately 3.5” diameter and are slightly over 1/8” thick. Version A and B are very similar in size, but vary slightly. Check the info above to determine which version you need for your system. Version B is slightly smaller than Version A. Manufactured and warrantied by Captain O-Ring LLC. Proudly assembled in the USA!