Discs are one of the types of sealing elements used by steel-mandrel pigs and are unique because of their bidirectional capability. They are designed to allow the pressure of the line to seat the outer sealing surface of the disc against the internal pipe surface to ensure positive seal. Discs are flexible so as to adapt to out-of-round or varying internal pipe diameters and can be easily manufactured to any desired diameter, thickness and bolting configuration without incurring a substantial cost to the molding process. This makes them ideal for special diameters, such as heavy-wall pipe. Styles include standard, guide, sealing and spacer types.