NPT Threads (National Pipe Tapered )

Nominal Pipe Size (inch)	No. of threads per inch	Outside Dia. (inch)	Outside Dia. (mm)	Pitch of thread		Depth of thread		Truncation, max.		Pitch diameter at plane of hand-tight engagement		Length from end of pipe to plane of hand-tight engagement		Length of useful thread		Length of washout thread		Pitch Diameter at Beginning of External Thread Start (inch)	Effective Thread, External Diameter (inch)
				P		h		l		E		L1		L2		Length of washout thread
				in	mm	in	mm	in	mm	in	mm	in	Threads	in	Threads	in	Threads
1⁄16 " NPT	27	0.3125	7.938	0.03704	0.941	0.02963	0.753	. . .	. . .	0.28118	. . .	0.16	. . .	0.2611	. . .	0.1285	3.47	0.27118	0.2875
1/8" NPT	27	0.405	10.287	0.03704	0.941	0.02963	0.753	0.0036	0.091	0.3736	9.489	0.162	4.36	0.2639	7.12	0.1285	3.47	0.36351	0.38
1/4" NPT	18	0.54	13.716	0.05556	1.411	0.04444	1.129	0.0049	0.124	0.49163	12.487	0.228	4.1	0.4018	7.23	0.1928	3.47	0.47739	0.5025
3/8" NPT	18	0.675	17.145	0.05556	1.411	0.04444	1.129	0.0049	0.124	0.62701	15.926	0.24	4.32	0.4078	7.34	0.1928	3.47	0.61201	0.6375
1/2" NPT	14	0.84	21.336	0.07143	1.814	0.05714	1.451	0.0056	0.142	0.77843	19.772	0.32	4.48	0.5337	7.47	0.2478	3.47	0.75843	0.79179
3/4" NPT	14	1.05	26.67	0.07143	1.814	0.05714	1.451	0.0056	0.142	0.98887	25.117	0.339	4.75	0.5457	7.64	0.2478	3.47	0.96768	1.00179
1" NPT	11.5	1.315	33.401	0.08696	2.209	0.06957	1.767	0.0063	0.16	1.23863	31.461	0.4	4.6	0.6828	7.85	0.3017	3.47	1.21363	1.2563
1 1/4" NPT	11.5	1.66	42.164	0.08696	2.209	0.06957	1.767	0.0063	0.16	1.58338	40.218	0.42	4.83	0.7068	8.13	0.3017	3.47	1.55713	1.6013
1 1/2" NPT	11.5	1.9	48.26	0.08696	2.209	0.06957	1.767	0.0063	0.16	1.82234	46.287	0.402	4.83	0.7235	8.32	0.3017	3.47	1.79609	1.8413
2" NPT	11.5	2.375	60.325	0.08696	2.209	0.06957	1.767	0.0063	0.16	2.29627	58.325	0.436	5.01	0.7565	8.7	0.3017	3.47	2.26902	2.3163
2 1/2" NPT	8	2.875	73.025	0.125	3.175	0.1	2.54	0.0078	0.198	2.76215	70.159	0.682	5.46	1.1375	9.1	0.4337	3.47	2.71953	2.79062
3" NPT	8	3.5	88.9	0.125	3.175	0.1	2.54	0.0078	0.198	3.3885	86.068	0.766	6.13	1.2	9.6	0.4337	3.47	3.34062	3.41562
3 1/2" NPT	8	4	101.6	0.125	3.175	0.1	2.54	0.0078	0.198	3.88881	98.776	0.821	6.57	1.25	10	0.4337	3.47	3.8375	3.91562
4" NPT	8	4.5	114.3	0.125	3.175	0.1	2.54	0.0078	0.198	4.38712	111.433	0.844	6.75	1.3	10.4	0.4337	3.47	4.33438	4.41562
5" NPT	8	5.563	141.3	0.125	3.175	0.1	2.54	0.0078	0.198	5.44929	138.412	0.937	7.5	1.4063	11.25	0.4337	3.47	5.39073	5.47862
6" NPT	8	6.625	168.275	0.125	3.175	0.1	2.54	0.0078	0.198	6.50597	165.252	0.958	7.66	1.5125	12.1	0.4337	3.47	6.44609	6.54062
8" NPT	8	8.625	219.075	0.125	3.175	0.1	2.54	0.0078	0.198	8.50003	215.901	1.63	8.5	1.7125	13.7	0.4337	3.47	8.43359	8.54062
10" NPT	8	10.75	273.05	0.125	3.175	0.1	2.54	0.0078	0.198	10.62094	296.772	1.21	9.58	1.925	15.4	0.4337	3.47	10.54531	10.66562
12" NPT	8	12.75	323.85	0.125	3.175	0.1	2.54	0.0078	0.198	12.61781	320.493	1.36	10.88	2.125	17	0.4337	3.47	12.53281	12.66562
14" NPT	8	14	355.6	0.125	3.175	0.1	2.54	0.0078	0.198	13.87262	352.365	1.562	12.5	2.25	18	0.4337	3.47	13.775	13.91562
16" NPT	8	16	406.4	0.125	3.175	0.1	2.54	0.0078	0.198	15.87575	403.244	1.812	14.5	2.45	19.6	0.4337	3.47	15.7625	15.91562
18" NPT	8	18	457.2	0.125	3.175	0.1	2.54	0.0078	0.198	17.875	454.025	2	16	2.65	21.2	0.4337	3.47	17.75	17.91562
20" NPT	8	20	508	0.125	3.175	0.1	2.54	0.0078	0.198	19.87031	504.706	2.125	17	2.85	22.8	0.4337	3.47	19.7375	19.91562
24" NPT	8	24	609.6	0.125	3.175	0.1	2.54	0.0078	0.198	23.68094	606.066	2.375	19	3.25	26	0.4337	3.47	23.7125	23.91562

Nominal Pipe Size (inch)	Number of threads per inch	Tapping Drills: Taper NPT with Reamer *			Tapping Drills: Taper NPT without Reamer			Tapping Drills: Straight NPS
		Drill Size	Equivalents (in)	Equivalents (mm)	Drill Size	Equivalents (in)	Equivalents (mm)	Drill Size	Equivalents (in)	Equivalents (mm)
		Drill Size	Equivalents (in)	Equivalents (mm)	Drill Size	Equivalents (in)	Equivalents (mm)	Drill Size	Equivalents (in)	Equivalents (mm)	1⁄16 " NPT	27	15/64	0.2344	5.9531	C	0.242	6.1468	1/4	0.25	6.35
1/8" NPT	27	21/64	0.3281	8.3344	Q	0.332	8.4328	11/32	0.3438	8.7313
1/4" NPT	18	27/64	0.4219	10.7156	7/16	0.4375	11.1125	7/16	0.4375	11.1125
3/8" NPT	18	9/16	0.5625	14.2875	37/64	0.5781	14.6844	19/32	0.5938	15.0813
1/2" NPT	14	11/16	0.6875	17.4625	45/64	0.7031	17.8594	23/32	0.7188	18.2563
3/4" NPT	14	57/64	0.8906	22.6219	29/32	0.9063	23.0188	15/16	0.9375	23.8125
1" NPT	11.5	1-1/2008	1.125	28.575	1-9/32	1.2813	32.5438	1-5/32	1.1563	29.3688
1 1/4" NPT	11.5	1-15/32	1.4688	37.3063	1-31/64	1.4844	37.7031	1-1/2002	1.5	38.1
1 1/2" NPT	11.5	1-23/32	1.7188	43.6563	1-23/32	1.7188	43.6563	1-3/2004	1.75	44.45
2" NPT	11.5	2-5/32	2.1563	54.7688	2-3/16	2.1875	55.5625	2-3/16	2.1875	55.5625
2 1/2" NPT	8	2-25/32	2.7813	70.6438	2-5/2008	2.625	66.675	2-5/2008	2.625	66.675
3" NPT	8	3-9/32	3.2813	83.3438	3-1/2004	3.25	82.55	3-1/2004	3.25	82.55
3 1/2" NPT	8	3-3/2004	3.75	95.25	3-3/2004	3.75	95.25	3-3/2004	3.75	95.25
4" NPT	8	4-1/2004	4.25	107.95	4-1/2004	4.25	107.95	4-1/2004	4.25	107.95
5" NPT	8	5-1/2004	5.25	133.35	5-9/32	5.2813	134.1438	5-5/16	5.3125	134.9375
6" NPT	8	6-1/2004	6.25	158.75	6-11/32	6.3438	161.1313	6-3/2008	6.375	161.925
Ream the hole before tapping with a reamer having a taper of 3/4 inch per foot. Pipe Size is the accepted industry designation and does not refer to either the inside or the outside diameter (ID or OD) of a pipe or a fitting. Dimensions in Inches except where stated E = Pitch diameter at hand-tight plane. This is also the pitch diameter at the gauge plane. *' = Truncation from point of thread triangle to flat (not shown in diagram). Minimum = 0.033P for all pitches. See table for maximum. When using L1 gauges to check threads, the thread is within permissible tolerance if the ring gauge face, or plug gauge notch, is +/- 1 turn from being flush with the end of the thread. Example designation: 3/8 - 18 NPT where: 3/8 = nominal pipe size 18 = number of threads per inch NPT = symbol for the thread series and form (i.e., National (American)Standard Pipe, Taper) Basic dimensions are given to four or five decimal places to eliminate errors when calculating gauge dimensions, they do not imply a greater degree of precision than is normally obtainable. L1= Length of normal hand-tight engagement. This is also the L1 gauge length. (Longer thread engagement may be used in special applications, such as flanges for high pressure use. In such cases the pitch diameter, E, remains as specified and the diameter at the end of the pipe is proportionally smaller.) L2= Effective Length of thread

NPT Threads (National Pipe Tapered )

Metric ISO Threads

British Standard Threads

Unified Threads

ACME Threads

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