In-line NPT connections are standard. These metering tubes are manufactured from solid cast acrylic rod stock. The end fittings thread into metering tubes and O-rings are used to achieve a positive seal. The tubes are precision-bored to close tolerances for function, then polished for aesthetics Scales are direct reading (GPM-water or SCFM-air) standard, other scales are available. Specifications : Capacities: Water–to 200 GPM; Air–to 245 SCFM. Scale length: 5" (127 mm).