Search: Process

6 results

Search results

NPT vs. BSP Pipe

While NPT threads are common in the United States, BSP threads are widely used in many other countries.  I have found that my Japanese-built injection mold presses have predominantly BSP fittings. 

American National Pipe - NPT/NPS

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.

British Standard Pipe - BSP

BSP: British Standard Pipe

BSP pipe, Like American National pipe (NPT, NPSM), is designated by trade size, rather than actual diameter, which is approximately equal to the thread's Major Diameter in the table below.

There are two types of BSP threads:

  • BSPT: British Standard Pipe Taper -also known as "R" or "Rc" threads
  • BSPP: British Standard Pipe Parallel -also known as "G" or "Rp" threads

Both styles have the same thread angle, shape, and pitch (threads per inch).  However, BSPT threads are tapered and BSPP threads are straight (parallel).  BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form).

Here are the actual thread dimension data for BSPP and BSPT threads.  The major diameter is a bit larger smaller than the actual OD of the pipe, and the minor diameter should be very close to what you would measure inside the female threaded end of a fitting.  Note that the Gage Length dimension pertains only to the BSPT (tapered) thread. 

Thread Type Compatibility

In order for two components to fit properly, thread types must be compatible. See the list below for thread types that can be used together.

 ** We had previously indicated GHT as compatible with 3/4-NH.  This was incorrect.  Oops... sorry.

AS568B O-Ring Data

Click this title (just above this text) and then follow the index links below or to the right for more dimensional data on the various o-ring series.

What I've shown here are some generally useable groove design data, but if you really want the whole story of oring seal design, this Parker handbook is the real authority.  Serious readers only.

The following tables give the gland dimensions for static and dynamic (reciprocating) applications.

Static O-Ring Axial (Face Seal) Glands
AS568B Cross Gland Squeeze Groove Width Groove
Section Depth Inches % Liquids Gases Radius
-004 thru -050 .070±.003 .050    .054 .013   .023 19     32 .101   .107 .084   .089 .005   .015
-102 thru -178 .103±.003 .074   .080 .020   .032 20     30 .136   .142 .120   .125 .005   .015
-201 thru -284 .139±.004 .101   .107 .028   .042 20     30 .177   .187 .158   .164 .010   .025
-309 thru -395 .210±.005 .152   .162 .043   .063 21     30 .270   .290 .239   .244 .020   .035
-425 thru -475 .275±.006 .201   .211 .058   .080 21     29 .342   .362 .309   .314 .020   .035

 

Static O-Ring Radial Glands
AS568B Cross Gland Squeeze Diametral Groove Width Groove
Section Depth Inches % Clearance 0 BR 1 BR 2 BR Radius
-004 thru -050 .070±.003 .050    .052 .015    .023 22    32 .002    .005 .093    .098 .138    .143 .205    .210 .005   .015
-102 thru -178 .103±.003 .081    .083 .017    .025 17    24 .002    .005 .140    .145 .171    .176 .238    .243 .005   .015
-201 thru -284 .139±.004 .111    .113 .022    .032 16    23 .003    .006 .187    .192 .208    .213 .275    .280 .010   .025
-309 thru -395 .210±.005 .170     .173 .032    .045 15    21 .003    .006 .281    .286 .311    .316 .410    .415 .020   .035
-425 thru -475 .275±.006 .226    .229 .040    .055 15    20 .004    .007 .375    .380 .408    .413 .538    .543 .020   .035

 

Dynamic O-Ring Reciprocating Glands
AS568B Cross Gland Squeeze Diametral Groove Width Groove
Section Depth Inches % Clearance 0 BR 1 BR 2 BR Radius
-004 thru -050 .070±.003 .055    .057 .010    .018 15    25 .002    .005 .093    .098 .138    .143 .205    .210 .005   .015
-102 thru -178 .103±.003 .088    .090 .010    .018 10    17 .002    .005 .140    .145 .171    .176 .238    .243 .005   .015
-201 thru -284 .139±.004 .121    .123 .012    .022 9      16 .003    .006 .187    .192 .208    .213 .275    .280 .010   .025
-309 thru -395 .210±.005 .185    .188 .017    .030 8       14 .003    .006 .281    .286 .311    .316 .410    .415 .020   .035
-425 thru -475 .275±.006 .237    .240 .029    .044 11    16 .004    .007 .375    .380 .408    .413 .538    .543 .020   .035

Comparison of hose stock types

 Comparison of hose stock types

Chemical name
Neoprene
Nitrile (Buna-N)
Butyl
Hypalon
EPDM
CPE
ASTM-SE designation
SC
SB
R
TB
R
None
SAE J14 & SAE J200
BC
BG
AA
CE
AA
None
Flame resistance
Very good
Poor
Poor
Good
Poor
Good
Petroleum base oils
Good
Excellent
Poor
Good
Poor
Very good
Diesel fuel
Good to excellent
Excellent
Poor
Poor
Poor
Very good
Resistance to gas permeation
Good
Good
Outstanding
Good to excellent
Fair to good
Good
Weather
Good to excellent
Poor
Excellent
Very good
Excellent
Good
Ozone
Good to excellent
Poor for tube
Good for cover
Excellent
Very good
Outstanding
Good
Heat
Good
Good
Excellent
Very good
Excellent
Excellent
Low temperature
Fair to good
Poor to fair
Very good
Poor
Good to excellent
Good
Water-oil emulsions
Excellent
Excellent
Good
Good
Poor
Excellent
Water-glycol emulsions
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Diesters
Poor
Poor
Excellent
Fair
Excellent
Very good
Phosphate esters
Fair for cover
Poor
Good
Fair
Very good
Very good
Phosphate ester based emulsions
Fair for cover
Poor
Good
Fair
Very good
Very good

 
Pipe Size
Pitch  (Threads/Inch)
NPT/NPS
BSP
 1/16"
27
---
 1/8"
27
28
 1/4"
18
19
 3/8"
18
19
 1/2"
14
14
 5/8"
---
14

 
Pipe Size
Pitch  (Threads/Inch)
NPT/NPS
BSP
 3/4"
14
14
1"
11 1/2
11
1 1/4"
11 1/2
11
1 1/2"
11 1/2
11
2"
11 1/2
11
2 1/2"
8
11

 
Pipe Size
Pitch  (Threads/Inch)
NPT/NPS
BSP
3"
8
11
3 1/2"
8
11
4"
8
11
5"
8
11
6"
8
11
8"
8
---