Smith-Blair 411-045002-003 4" Steel Fabricated Coupling - Smith-Blair Steel Couplings offer many distinct advantages when installed in a piping system. Properly selected and installed flexible couplings maintain the continuity of the pipe system, retain the line contents under internal pressure and prevent infiltration under vacuum. Our couplings consist of one cylindrical sleeve with conical inner surfaces at each end; two resilient, wedge-shaped, specially-compounded rubber gaskets; two ring-shaped followers and a set of high-strength, low-alloy track-head, oval-neck, rolled-thread bolts with heavy hex nuts.