Oatey No-Calk flexible rubber rain collar has (2) openings - one with an actual 2-5/8" opening stretches to accommodate 3" vent/exhaust/flue pipes, and the other (accessible by removing inner ring with pliers) has an actual opening of 3-5/8", acommodating 4" vent/exhaust/flue pipe, including B-Vent, PVC, ABS, no-hub cast iron, Centrotherm Innoflue SW (Single Wall) & Concentric, and others. No-Calk design creates a watertight seal, requires no sealant and is UV-resistant. Can be slid over the existing vent/exhaust pipe as a secondary seal or to fix water leaks resulting from worn-out, deteriorating, damaged or cracked existing rain collar.