The 4" Wilkins 350DA is a double check detector assembly began production in 1998 and is still currently being produced. The body is constructed of epoxy coated ductile iron. Check assemblies are a plastic cam check design and springs are self contained. Spring tension does not need to be released to replace rubber discs. Retainer clips hold the checks in place. The 350 uses a single victaulic clamp style cover. The bypass uses a 3/4" Wilkins 950XL backflow preventer and a standard 5/8 X 3/4" Water meter. In 2004, the 350ADA model was introduced. The "A" used grooved connections between the body and gate valves. Please be sure which model you have because some repair parts are different. In 2010, all bronze parts (test cocks, bulkhead fittings, ect.) were transitioned to lead free bronze to adhere to new codes. No special tools are required for servicing.