Here is the latest from Home Depot posted on the 9th. They were installed on cast iron pipe, which is common on homes prior to 1965. The screws can be snugged up for a fit, but they will not penetrate the iron. 5 stars
Very well made vents which are easy to install. My vents are cast iron covered in lead so screws not usable but vent fits snuggly enough that screws not really needed. Roofing caulk line around base and good to go!