Oatey Gripper plugs mechanically expand to seal the end of a pipe and hold pressure when testing a piping system. They are constructed of durable glass reinforced ABS plastic and a natural rubber o-ring. The extra large wing nut makes installation easy without tools. Size: 4 In. Flange Material: Zinc Gasket Material: Rubber WARNING: Cancer and Reproductive Harm -www.P65Warnings.ca.gov. - Styrene