This package includes the Nu-Clear Canister Filter Replacement Cartridge, 25 Micron, for the Nu-Clear Canister Filter Model 533 and Nu-Clear Canister Filter Model 530, along with a Nu-Clear Canister Filter Replacement O-Ring and Inland Seas Super Lube Silicone Lube, 1cc. O-rings should be replaced once a year. Every time the 25 Micron Nu-Clear Canister Filter is cleaned, when putting the lid of the Filter back on you should lubricate the O-Ring with Inland Seas Super Lube Silicone Lube, 1cc. Cartridge dimensions: 8.5" wide and 8 3/8" tall. Center hole is 4" wide.