The Watts 957NRPDA and 957ZRPDA are reduced pressure detector assemblies (RPDA). They are available in 2 1/2″-10″ sizes and have been in production since 2000. Their bodies are made of stainless steel. The 957NRPDA is an “N” shaped device and the 957ZRPDA is a “Z” shaped device but they share the same parts. The 957NRPDA and 957ZRPDA currently utilize a 3/4″ 919 for the bypass assembly. A lead free version was introduced in 2013. The 957NRPDA and 957ZRPDA are private labels of the Ames C500N and C500Z.