Can someone explain pipe thread to me

Question

ex. in my hand is a 2" nipple i you mesure across its about 2 5/16 if you could mesure the botom of the threads across it would be about 2 1/8 - 2 3/16 how in the world do they come up calling this a 2" pipe it makes no sense what so ever

Answer 1

a 2" pipe means the pipe has a 2" inside diameter

the 2-5/16" is the pipe ouside diameter

the bottom of the thread you measured is the pitch diameter, in which they made the pipe by following a standard pipe thread dimensions.

Answer 2

In the US, pipe sizes of different material are not of the same dimension internally.  Rigid PVC plastic and steel pipe have the same OD sizes but differing wall thicknesses cause the ID to differ.  

PVC Schedule 40 is based upon standard steel pipe dimensions and   2" PVC or steel has a ID of 2.067 inches with comparable steel pipe wall thickness.  Sch 80 is based upon steam pipe and 2" has 1.939 ID.  

PVC SDR (Standard Dimension Ratio) pipe also has the same OD, but the wall thickness if a ratio.  2" SDR 26 will have a wall thickness 1/26 of the overall diameter, SDR 21 will have a wall thickness 1/21, etc.  2" SDR 26 has an ID of 2.193", SDR 21 2.149", SDR 17 2.095.

PE pipe is different yet and 2" has an ID of 2.067.  With PE pipe, the ID is the same but the wall thickness and OD differs with different pressure ratings.  

With PE pipe, the higher working pressure a pipe has, the greater the OD.   With PVC, the higher the working pressure, the smaller the ID the pipe has.  

There are yet other pipe sizes that makes life even more complicated.  For example, PVC pipe that is able to withstand hot water has a different ID and OD from cold water PVC.    

Answer 3

2.375" is the outside diameter of the pipe.

2 inch is nominal size of the thread.

2 1/8 - 2 3/16 at the bottom means at the end of a threaded nipple.

Threads per Inch , TPI - pitch :11-1/2

From above data , it is clear that it is a 2 INCH NPT Thread.

Standard=ANSI/ASME B1.20.1

Characteristics of NPT (also known as ANSI/ASME B1.20.1 Pipe Threads, General Purpose):

    * tapered thread 1deg 47'

    * truncation of roots and crests are flat

    * 60 degree thread angle

    * pitch is measured in threads per inch

Major diameter : 59.614 mm

Major diameter : 56.656 mm