The 8" Febco 856ST Series double check detector assemblies began production in 2011 and was discontinued in 2014. The 856ST was replaced by the LF856. Known as the "Master Series" the 856ST is constructed of epoxy coated ductile iron. Checks are a swing check type with self contained spring modules. Check seats are replaceable. Check discs are vulcanized rubber disc type. Bypass assembiy shall be 3/4" Watts 719. Parts do not interchange between 856ST and 856/LF856 models. Please be sure of your mdel before ordering parts. No special tools are required for servicing.