"Grip-Rib" design acts as a suction cup. Hard rubber ends are molded inside the plug, without seams, to prevent stem and end blow-off. All brass tire stem valves are uniquely molded in the plug end. This design prevents the stem from being pulled off. Durable chain eye is molded as part of the plug. Pull chain is strong, steel sash. Inflation and back pressure information is permanently molded in plug. Each PASCO "Sure Test" inflatable test plug has the patented "Grip-Rib" design. As the plug is inflated inside the pipe, the "Grip-Rib" acts as a suction cup to insure a positive seal.