Plumbing - NPT vs straight thread

[Donald]

Actually I have this going to a 3/4" NPT nipple on a tee on top the out and in and to 3/4" PVC male connector. They fit NPT or straight threads because the gasket does the sealing.

Just like your garden hose does though it has garden hose threads.

So given that the male is tapered and the female is straight thread, how much thread is the female grabbing.

 

[SHOZ]

So given that the male is tapered and the female is straight thread, how much thread is the female grabbing.

I'm not going to take it apart but it has been in place for near 40 years on two different water heaters and peak pressure is around 55 lbs. You don't have to get one. But that is exactly what they are made for.

 

[y_p_w]

So given that the male is tapered and the female is straight thread, how much thread is the female grabbing.

I believe it wedges the threads to form a tight seal, or at least that’s how it was explained to me. But the threads have to be extremely smooth. I still see conflicting info on whether or not pipe dope is a sealant or just a lubricant that just helps to improve the seal.

 

[SHOZ]

I don't use a sealant. You don't use one on the garden hose do you? Plenty of thread contact to get as tight as you want. It doesn't strip. Washer hoses too.

 

[burbguy82]

My guess is the nipple on top of your water heater was straight thread

no, all tapered threads

The nipple on my water heater is NPT. Tapered.

straight thread connector will work. 100%

 

[y_p_w]

I don't use a sealant. You don't use one on the garden hose do you? Plenty of thread contact to get as tight as you want. It doesn't strip. Washer hoses too.

A garden hose involves compression of a washer for a positive seal. However, I’ve heard of excessively tightened connections where the threads cracked in tapered threads.

 

[SHOZ]

A garden hose involves compression of a washer for a positive seal. However, I’ve heard of excessively tightened connections where the threads cracked in tapered threads.

The pipe I showed have plenty beefy threads and hex. It's not a garden hose connector.

 

[y_p_w]

The pipe I showed have plenty beefy threads and hex. It's not a garden hose connector.

You mentioned a garden hose.

 

[Rogueman2016s]

The thread was about NPT pipe nipple on water heater and the SS braided supply lines that are FIP.

yup

 

[burbguy82]

So given that the male is tapered and the female is straight thread, how much thread is the female grabbing.

more than 75% registration

 

[Rogueman2016s]

The HOT and COLD water connections are clearly marked and are ¾” NPT on all models. When connecting to the inlet/outlet ports, the use of ¾” female NPT tapered thread fittings with use of thread sealant is recommended.

https://products.geappliances.com › ...

Water Heaters - Water Supply Connections - ge kitchen appliances

Any further confusion hire a plumber​

 

[SHOZ]

You mentioned a garden hose.

In the way that it seals, aka the gasket. Although it is not garden hose gasket. It seals like the one you posted in #7.

 

[Donald]

With a male and female both straight thread you can keep screwing it in until the male is tightened against the gasket.

But if the male is NPT (tapered) the threading as it increases in diameter could prevent the male from fully tightening against the gasket.

Not saying it might not work but hard to believe someone would design it that way.

 

[Pablo]

I asked a very similar question a couple weeks ago about 2" NPT and a straight coupler. Works great from mechanical attachment. Not approved for gas!

EDIT: Forgot to add, I make sure the the end of the NPT pipe (nipple) in the type of fittings described here is square and flat as possible,

 

[CDX825]

With a male and female both straight thread you can keep screwing it in until the male is tightened against the gasket.

But if the male is NPT (tapered) the threading as it increases in diameter could prevent the male from fully tightening against the gasket.

Not saying it might not work but hard to believe someone would design it that way.

Here ya go. Been in service for 10 years now at my house and I have above normal water pressure. No leaks.

 

[oilcandave]

With a male and female both straight thread you can keep screwing it in until the male is tightened against the gasket.

But if the male is NPT (tapered) the threading as it increases in diameter could prevent the male from fully tightening against the gasket.

Not saying it might not work but hard to believe someone would design it that way.

Well that is the design. I don't use it nor recommend it. But they do work.. usually..