The Oatey® Mushroom Vent Cap is made of high-impact PVC and requires no assembly. It includes 3 hex-head bolts for ease of installation. The fully assembled mushroom vent cap fits 3 in. and 4 in. vent stacks to prevent debris, water and various critters from entering the vent pipe. Oatey products have earned the trust of plumbing professionals for over 100 years.