They are all hand built by our skilled craftsmen. The 1/4” minimum thickness solid elastomer tube is continuous with the flange face. Multiple plies of rubber impregnated high strength polyester or nylon tire cord form the first pressure reinforcement over the tube. Arch swell in response to pressure and arch migration are virtually eliminated by criss-crossed layers of reinforcement that pass over the arch and around steel or ductile iron rings embedded on both sides at the base of the arch. Body swell is controlled by high strength fabric or spiral steel wire. Large diameter joints are often built with steel rings in place of the wire when in addition to internal pressure, external pressure resistance is important. External pressure may come from deep burial, shallow embankment under roadways or joints inside tanks.