Part of OK-25 package, but just the one size. Sold in different quantities with or without silicone grease. Use silicone grease to delay o-ring rot. Replace every 3rd filter change or as needed.
Caution: Fits the new OB1 housing with an original Black o-ring. Older OB1 with original Blue o-ring needs smaller o-ring, part of K-4 package.
Caution: Fits the older U25 Series housing. The newer housings use a thicker 3/16″ inch o-ring.
