Used for a variety of applications, not limited to grease, fuels, refrigeration, water, oil gas, and hydraulic systems. If you are unsure as to which NPT thread size you have ,please reference this chart that show you the NPT thread size crossed over the your linear measurement in inches. Note:NPT cannot be accurately calvulated with a linear measuring tool like a Tape Measure, Ruler or Caliper. NPT Thread size is NOT determined by its outside thread diameter in inches.