Size 12. Like Superb Wrench, 2.5" x 20", this wrench fits housings on Pura UV20, Pura UVB, Flowmatic 2.5" x 20" housings and Pentek Big Blue 2.5" x 20" housings, including our Light Duty Whole House Filters.
Half-circle wrenches can fit into trickier spaces since they don't need to start at bottom of the housing.
(whole house & well units)