The DuraVent 4PPS-FS is a concentric firestop spacer that is designed to be used on your polypropylene vent system. This is to be used when penetrating floor levels. It is made for a double-wall construction and is corrosion-resistant. It has a size of 4 inches and is a two-piece design to make it easier to install on your system. For your venting needs, you are assured that DuraVent can offer you the best and high-quality products. Search yours now at PlumbersStock.com.