Mech 416 Cast Iron Soil Coupling.The simple and reliable couplings make it particular suitable for repair and extension projects.This ductile iron coupling is a two piece fitting with an EPDM sealing ring and zinc plated locking screws.This is the most commonly used coupling in the Mech 416 range, available in 50mm, 70mm, 100mm and 150mm size options.Hargreaves Mech 416 cast iron soil system is a fit and forget solution and offers a modern alternative to traditional soil systems, especially for industrial and commercial. buildings.