My main water line currently feeds into a water filter using a 3/4" FIP x 3/4" FIP x 24" braided stainless steel water heater connector line:

water heater connector http://www.hardwareworld.com/Water-Heater-Connector-~-24-pRNH8OE.aspx

I'm replacing the water filter with a new filtering system that has a plastic 3/4" NPT female thread. My understanding is that the 3/4" NPT female thread is really the same thread as a 3/4" FIP. Please correct me if I'm wrong on that.

The instructions for the new filter state that I should only use plastic fittings to connect the water supply to the filter. Using a metal fitting may damage the plastic threads of the filter inlet port.

So, what kind of fitting should I use to connect the stainless steel 3/4" FIP to the plastic female 3/4" inlet port. It would seem somewhat obvious that I need a 3/4" MIP to 3/4" MIP fitting. But, I'm not sure what material it would be. The filter instructions just say plastic, but I'm not sure which type of plastic I should be using. I'm also having a problem locating a fitting like this online regardless of material type. Where would I buy something like this?

This is a picture of my filter and I can tell that they have some type of fitting there to make the connection between the copper and the filter. I'm looking for something similar, but as described above, to connect to the water heater connector line:


Thank you in advance.

  • 2
    OMG you activated my tic. Aug 28, 2015 at 6:32
  • 1
    @TylerDurden sorry, I don't follow. Aug 28, 2015 at 12:41
  • FYI the reason you want a plastic male end to fit into a plastic female fitting is so that the female part doesn't crack. If the female end was metal you can use either plastic or metal male to fit inside. I know this both by reading and sadly experience.
    – aaron
    Aug 28, 2015 at 13:33
  • @TylerDurden, hilarious, I sympathize. Aug 28, 2015 at 17:24

1 Answer 1


You'll want a 3/4" nylon hex nipple. Commonly they're available in white, gray, and black, though other colors may be available. More importantly, you'll want to make sure the fittings are NSF/ANSI 61 compliant. NSF/ANSI 61 certifies that the fitting is suitable as a drinking water system component.

3/4" nylon hex nipple

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