This is a picture of a product called a Perma Boot. These are designed for rubber flashing, the bell at the bottom allows the rubber grommet to be covered. However, they are not designed for any use on a lead flashing. Note there is no screen at the top to keep animals out. The bell serves no purpose on lead flashing. Putting one of these on a lead flashed vent is the same as putting a pipe on it. Critter Quitters are designed for lead flashed piping and protect, repair, and seal the unit from animal entry.