To thread plastic and metal fittings together, the male fitting has to be plastic, and the female fitting has to be metal.
When fittings with a tapered thread such as NPT are tightened, the male fitting is compressed, and the female fitting is stretched (tensile stress). Most materials generally have a higher compressive strength than tensile strength. This is why the female fitting is the one that will crack when over-tightened. Therefore the female fitting must be stronger than the male fitting. Metals are stronger than plastics. The female fitting has to be metal, and the male fitting plastic.
Please note that mixing metal and plastics is not highly recommended and should be avoided if possible.
Title: Can you thread plastic and metal NPT fittings together?
Description: Combining metal and plastic fittings.
Published: 1/29/2008
Last Edited: 12/29/2022
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