I don't have a Watts "block" BUT these filters are standard size cartridges and will fit other brand blocks. - remove old medium - insert new medium - some waterproof grease and screw on again. Not too complicated process. I also bought some spare o-rings in case the existing ones leak after reinstalling (good to have on hand). After flushing/refilling the system, the filters did their job with no noticeable difference in water quality. Well-known brand filters.
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