The "3/4" BSPF Nut & 3/8" Barbed Straight Adapter In Plastic with Washer" is a plumbing adapter that allows you to connect a 3/4 inch British Standard Pipe Fine (BSPF) female thread to a 3/8 inch barbed fitting. The adapter is made of plastic and comes with a washer to provide a secure seal. This type of adapter is commonly used in water supply systems and irrigation applications.