Npt Thread: 3/8" Npt x 18 Tpi Male (Actual Nominal Thread Size 5/8") to Npt Thread: 1/4" Npt x 18 Tpi Female (Actual Nominal Thread Size 1/2") pipe bushings allow for quick conversion and adapting various sizes of fittings, gauges, probes, sensors and instrumentation devices. Our fittings are reusable and can be used for applications involving pneumatics, vacuum, and general fluid handling. These brass fittings are an economical and durable solution to your piping and plumbing needs.