ASME B1.20.1-2013 pdf download
ASME B1.20.1-2013 pdf download.Pipe Threads,General Purpose(Inch).
6 SPECIFICATIONS FOR STRAIGHT PIPE THREADS FOR MECHANICAL JOINTS; NPSM, NPSL
6.1 Straight Pipe Threads for Mechanical Joints
In addition to pressure-tight pipe joints, for which taper external threads and taper or straight internal threads can he used, there are mechanical joints where straight pipe threads are used. Their pitch diameters and root and crest truncations vary as described below. These types of joints are as follows:
(a) free-fitting mechanical joints for fixtures, Table 6, both external and internal, NPSM
(b) loose-fitting mechanical joints with lock-nuts, Table 7, both external and internal, NPSL
6.1.1 Thread Designations. These threads are designated in accordance with para. 1.3.1 as follows:
1427 NPSM
‘4-27 NPSL
6.1.2 Pitch and Flank Angle. The pitch and flank angle are the same as the corresponding dimensions of the taper pipe thread described in section 3.
6.1.3 Diameter of Thread. The basic pitch diameter for both the external and internal threads is equal to E, of Table 2, which is the same as the large end of the internal NPT thread.
6.2 Free-Fitting Mechanical Joints for Fixtures, NPSM
Pipe is often used for special applications where there are no internal pressures and, consequently, no sealing requirements. Also, straight pipe threads are sometimes found more suited or convenient where straight thread joints are required for mechanical assemblies. In these cases, NPSM threads can be used, creating a reasonably close fit of matmg parts. The dimensions of these threads are given in Table 6. Gaging is described in para. 6.4.
6.3 Loose-Fitting Mechanical Joints With Locknuts, NPSL
The American National Standard External Locknut Thread is designed to produce a pipe thread having the largest diameter that is possible to cut on standard pipe. Ordinarily, straight internal threads are used with these straight external threads, providing a loose fit. The dimensions of these threads are given in Table 7. It will be noted that the maximum major diameter of the external thread is slightly greater than the nominal outside diameter of the pipe. The normal manufacturer’s variation in pipe diameter provides for this increase. One application of a taper pipe thread in combination with a locknut thread that has been in use for some time is that shown in Table 7. It consists of the nipple threaded joint used to connect standpipes with the floor or wall of a water supply tank.
6.4 Gaging for NPSM and NPSL Threads
Gaging to properly control the production of these straight threads should be through the use of GO and NOT GO gages or indicating type gages.
6.4.1 GO Gaging. The GO size is acceptable when the GO thread gage (plug or ring) freely engages the full threaded length of the product.
6.4.2 NOT GO Gaging. The NOT GO size is acceptable when the NOT GO thread gage (plug or ring) applied to the product thread does not enter more than three complete turns. The gage should not be forced. Special conditions, such as exceptionally thin or ductile material, small number of threads, etc., may necessitate modification of this practice.
6.4.3 Indicating Gages. When using indicating gages for straight threads, refer to ASME B1.2 for use.
6.4.4 Gage Dimensions. Gages used for NPSM shall be made to the pitch diameter limits specified in Table 6. Gages used for NPSL shall be made to the pitch diameter limits specified in Table 7. These gages shall be made in accordance with standard practice for straight thread gages as outlined in ASME B1.2. The minimum major diameter of the GO thread plug gage or internal functional indicating gage shall be equal to the minimum pitch diameter of the internal thread plus an amount equal to O.64951905P. The maximum major diameter of the NOT GO thread plug gage shall be equal to the maximum pitch diameter of the internal thread plus an amount equal to O.43301270P. The maximum minor diameter of the GO thread ring gage or external functional diameter indicating gage shall be equal to the maximum pitch diameter of the external thread minus an amount equal to O.43301300P. The minimum minor diameter of the NOT GO thread ring gage shall be equal to the minimum pitch diameter of the external thread minus an amount equal to O.21650635P.