Steam

Steam► Book page

Hose is like flexible tubing, but it should generally be considered as PIPE.

Hose is sized by its Inside Diameter. (A notable exception to this is the case of FIRE HOSE, which is often sized by its O.D. due to its associated fitments, many of which use the O.D. as their determinant diameter.)

Hose is most typically (and traditionally) made of rubber, though modern technology has brought us myriad new materials suitable for various working fluids and physical working criteria.

American National pipe (NPT, NPS), Like British Standard Pipe (BSP), is designated by trade size, rather than actual diameter, as shown in the table below.

There are two basic types of National pipe threads:

  • NPT: National Pipe Taper
  • NPS: National Pipe Straight

NPT threads are also sometimes referred to as

  • MIP (Male Iron Pipe)
  • FIP (Female Iron Pipe)
  • IPT (Iron Pipe Thread)
  • FPT (Female Pipe Thread)
  • MPT (Male Pipe Thread)

Note that these references are somewhat casual, and might possibly be used in reference to NPS instead of NPT.

Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch).  However, NPT threads are tapered and NPS threads are straight (parallel).  Both threads have a 60° included angle and have flat peaks and valleys (this is a Sellers thread form).

If you've worked with pipe much at all, you've probably noticed that the size of the pipe isn't really what size the pipe is.  Unlike tubing, which is generally specified by its OD, or hose, which is generally specified by its ID, pipe is specified by something else... its Trade Size.  So when you say "3/4 pipe," you're actually saying "pipe whose OD is a little more than an inch, and whose ID is about 53/64."  -that is, if you are talking about schedule 40 pipe, which is generally what is used for most plumbing applications.

Pipe dimensions are specified by trade size and schedule, according to the following table.  Note that while British Standard Pipe dimensions are similar, they are not equivalent to the American Standard Pipe Sizes.  See NPT vs. BSP Pipe for thread comparisons.

Steam► Specs and Standards

ISO 228-1

Pipe threads where pressure-tight joints are not made on the threads -- Part 1: Dimensions, tolerances and designation

This is the specification in force as of 2000 for BSPP threaded appliances.

souce: ISO 228-1:2000