NPT adaptors are male threaded adaptors that are used to connect two different sized pipes.
NPT adaptors are commonly used on our systems to bridge the connection between the bypass assembly (push/oull handle) and your home plumbing lines.
NPT fittings are listed by the "standard" inner diameter (I.D.) of the fitting. They can be found at most hardware stores. Below is a photo example of a 3/4" to 1" NPT adaptor: