ASME B1.20.1-2013 pdf – Pipe Threads, General Purpose (Inch)
ASME B1.20.1-2013 pdf – Pipe Threads, General Purpose (Inch).
4.1.2 DImensions and Limits of Size. The dimensions and pitch diametei limits of ste are specified in Table 4. The pitch diameter sizes correspond to the gagnig tolerance of one and turns large or small of the NPT E. The major and minor diameters vary with the pitch diameter, as the American National Standard Pipe Thread form is maintained within the turn tolerances shown in Table 1.
4.2 Gaging NPSC Internal Threads
Internal taper thread gages in accordance with section 7 shall be used to gage NPSC straight internal pipe threads.
4.2.1 L1 Plug Gage. The L, plug gage and internal product thread are screwed together hand-tight and the position relative to the basic step o4 the gage is noted. This is the standoff. The NPSC tolerance for the standoff Is i1A turns (or ±I pitch, as shown in column 4 of Table 2) from the basic step of the plug gage See paras. 22.214.171.124 and 126.96.36.199 for chamfered threads.
42.2 L1 Internal Indicating Gage. When product is engaged in an indicating gage set with a master gage. readings indicate the diametral variation from basic, The tolerance from basic is the diametral equkalent to ±l4 pitches (or ±43.0625/n. as shown in column 23 of Table 2). See paras 188.8.131.52 and 184.108.40.206 for chamfered threads.
6.3 Loose4itting Mechanical joints With Locknuts, NPSL
The American National Standard External Locknut Thread is designed to produce a pipe thread hosing 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 st.rndplpes 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 sii.e is acceptable when the NOT GO thread gage (plug or ring) applied to the product thread does riot 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 81.2 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 BlZ. 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 0.649519051’. 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 0.433012701’. The maximum minor diameter of the (() 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 0.4330l3O01 The minimum minor diameter ol the N(JI (0 thread ring gage shall be equal to the minimum pitch diameter of the external thread minus an amount equal to 35P.