Faria Oil Pressure Sender 1/8" NPTOil Pressure Sender 1 8" NPT Engines or transmissions equipped with a low oil pressure switch that activates a warning light require an appropriate T pipe fitting to accommodate both pressure sender and warning light. Most oil pressure sending units have 1 8 NPT pipe threads and are usually mounted in the engines block. If the block or transmission case has a larger pipe size, an appropriate bushing may be used without affecting pressure sensing