Whats the difference

Yesterday I was chasing some pipe threads in some cast iron. I picked a 3/8 X 18 NPS out of my collection and it would not fit in the hole where I wanted to clean up the threads. I went back and picked another tap that said 3/8 X 18 NPT and had no problem starting the tap in the hole. What does NPS mean.
 
npt is a tapered thread.
nps is a straight thread. and would need a sealing gasket or ring.
 
(quoted from post at 11:28:08 02/03/16) npt is a tapered thread.
nps is a straight thread. and would need a sealing gasket or ring.

Hummm, learn something everyday. I'm 76 years old and never heard of straight pipe threads. I always thought "NPT" was for National Pipe Thread. I knew they were tapered but didn't know that is what the "T" was for.
 
(quoted from post at 16:50:26 02/03/16)
(quoted from post at 11:28:08 02/03/16) npt is a tapered thread.
nps is a straight thread. and would need a sealing gasket or ring.

Hummm, learn something everyday. I'm 76 years old and never heard of straight pipe threads. I always thought "NPT" was for National Pipe Thread. I knew they were tapered but didn't know that is what the "T" was for.
Well, it does stand for National Pipe Thread, which is a tapered thread. NPS stands for National Pipe Size, which matches the OD of pipe, so a 1" NPS thread would be like a thread for a 1.315" bolt. Otherwise, an NPS tap is a straight tap.
 
It's late, NPS stands for Nominal Pipe Size, which is not the pipe outside diameter, or the inside diameter although it is close to inside sometimes. 3/8 NPS is 0.675" outside. 3/8 bolt is 0.375". 3/8" pipe internal diameter is 0.493 for standard pipe and 0.423" for schedule 80. Even though lots of folks think the nominal size is the internal diameter.
 
Actually, nominal pipe size used to be internal diameter. But that was many years ago. As metalurgy improved, engineers found that they could make the same strength with less material. Since pipe is threaded on the outside, they kept that the same to match with fittings & saved on material by increasing the inside diameter.

Willie
 
I was shopping in a thrift shop and found a new Delta Shower head for $2.00. that normally sold for $60. It leaked at the threads and I discovered it was missing the sealing ring and had straight threads. Three wraps of Teflon tape made it seal.
 
(quoted from post at 04:58:16 02/04/16) It's late, NPS stands for Nominal Pipe Size, which is not the pipe outside diameter, or the inside diameter although it is close to inside sometimes. 3/8 NPS is 0.675" outside. 3/8 bolt is 0.375". 3/8" pipe internal diameter is 0.493 for standard pipe and 0.423" for schedule 80. Even though lots of folks think the nominal size is the internal diameter.

You can measure say 1" pipe and never find a dimension that is 1"; unless you cut it 1" long. This has to have an English angle to it. I have some Whitworth tools and a 1/2" tool doesn't measure 1/2" across the flats or corners on a socket.
 

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