Cherne® Gripper Mechanical Plug by OateyDesigned to test drain, vent and waste systems to 17 PSI backpressureExtra large zinc wing nut for ease of tightening. No wrench requiredNatural rubber O-ring for excellent expansion and memoryABS glass-reinforced plates for added strengthMade of rust and corrosion resistant materialsAvailable in sizes:  1-1/2", 2", 3", and 4"