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MARYLAND METRICS
THREAD DATA CHARTS

NATIONAL PIPE TAPERED THREAD (NPT)
NPT Thread - American Standard Taper Pipe Thread (ANSI/ASME B1.20.1), Taper 1:16
Thread Form Data - Basic Dimensions of American National Standard Taper Threads, NPT (National Pipe Tapered)

Nominal Pipe Size (inch) Number of threads per inch Outside Diameter (inch) Outside Diameter (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      
        in mm in mm in mm in mm in Threads in Threads in Threads    
1⁄16 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 0.28750
1/8" 27 0.405 10.287 0.03704 0.941 0.02963 0.753 0.00360 0.091 0.37360 9.489 0.162 4.36 0.2639 7.12 0.1285 3.47 0.36351 0.38000
1/4" 18 0.540 13.716 0.05556 1.411 0.04444 1.129 0.00490 0.124 0.49163 12.487 0.228 4.10 0.4018 7.23 0.1928 3.47 0.47739 0.50250
3/8" 18 0.675 17.145 0.05556 1.411 0.04444 1.129 0.00490 0.124 0.62701 15.926 0.240 4.32 0.0478 7.34 0.1928 3.47 0.61201 0.63750
1/2" 14 0.840 21.336 0.07143 1.814 0.05714 1.451 0.00560 0.142 0.77843 19.772 0.320 4.48 0.5337 7.47 0.2478 3.47 0.75843 0.79179
3/4" 14 1.050 26.670 0.07143 1.814 0.05714 1.451 0.00560 0.142 0.98887 25.117 0.339 4.75 0.5457 7.64 0.2478 3.47 0.96768 1.00179
1" 11.5 1.315 33.401 0.08696 2.209 0.06957 1.767 0.00630 0.160 1.23863 31.461 0.400 4.60 0.6828 7.85 0.3017 3.47 1.21363 1.25630
1-1/4" 11.5 1.660 42.164 0.08696 2.209 0.06957 1.767 0.00630 0.160 1.58338 40.218 0.420 4.83 0.7068 8.13 0.3017 3.47 1.55713 1.60130
1-1/2" 11.5 1.900 48.260 0.08696 2.209 0.06957 1.767 0.00630 0.160 1.82234 46.287 0.402 4.83 0.7235 8.32 0.3017 3.47 1.79609 1.84130
2" 11.5 2.375 60.325 0.08696 2.209 0.06957 1.767 0.00630 0.160 2.29627 58.325 0.436 5.01 0.7565 8.70 0.3017 3.47 2.26902 2.31630
2-1/2" 8 2.875 73.025 0.12500 3.175 0.10000 2.540 0.00780 0.198 2.76215 70.159 0.682 5.46 1.1375 9.10 0.4337 3.47 2.71953 2.79062
3" 8 3.500 88.900 0.12500 3.175 0.10000 2.540 0.00780 0.198 3.38850 86.068 0.766 6.13 1.2000 9.60 0.4337 3.47 3.34062 3.41562
3-1/2" 8 4 101.600 0.12500 3.175 0.10000 2.540 0.00780 0.198 3.88881 98.776 0.821 6.57 1.2500 10.00 0.4337 3.47 3.83750 3.91562
4" 8 4.5 114.300 0.12500 3.175 0.10000 2.540 0.00780 0.198 4.38712 111.433 0.844 6.75 1.3000 10.40 0.4337 3.47 4.33438 4.41562
5" 8 5.563 141.300 0.12500 3.175 0.10000 2.540 0.00780 0.198 5.44929 138.412 0.937 7.50 1.4063 11.25 0.4337 3.47 5.39073 5.47862
6" 8 6.625 168.275 0.12500 3.175 0.10000 2.540 0.00780 0.198 6.50597 165.252 0.958 7.66 1.5125 12.10 0.4337 3.47 6.44609 6.54062
8" 8 8.625 219.075 0.12500 3.175 0.10000 2.540 0.00780 0.198 8.50003 215.901 1.630 8.50 1.7125 13.70 0.4337 3.47 8.43359 8.54062
10" 8 10.750 273.050 0.12500 3.175 0.10000 2.540 0.00780 0.198 10.62094 296.772 1.210 9.58 1.9250 15.40 0.4337 3.47 10.54531 10.66562
12" 8 12.750 323.850 0.12500 3.175 0.10000 2.540 0.00780 0.198 12.61781 320.493 1.360 10.88 2.1250 17.00 0.4337 3.47 12.53281 12.66562
14" 8 14 355.600 0.12500 3.175 0.10000 2.540 0.00780 0.198 13.87262 352.365 1.562 12.50 2.2500 18.00 0.4337 3.47 13.77500 13.91562
16" 8 16 406.400 0.12500 3.175 0.10000 2.540 0.00780 0.198 15.87575 403.244 1.812 14.50 2.4500 19.60 0.4337 3.47 15.76250 15.91562
18" 8 18 457.200 0.12500 3.175 0.10000 2.540 0.00780 0.198 17.87500 454.025 2.000 16.00 2.6500 21.20 0.4337 3.47 17.75000 17.91562
20" 8 20 508.000 0.12500 3.175 0.10000 2.540 0.00780 0.198 19.87031 504.706 2.125 17.00 2.8500 22.80 0.4337 3.47 19.73750 19.91562
24" 8 24 609.600 0.12500 3.175 0.10000 2.540 0.00780 0.198 23.68094 606.066 2.375 19.00 3.2500 26.00 0.4337 3.47 23.71250 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)
1⁄16 27 15/64" 0.2344 5.9531 C 0.242 6.1468 1/4" 0.25 6.35
1/8" 27 21/64" 0.3281 8.3344 Q 0.332 8.4328 11/32" 0.3438 8.7313
1/4" 18 27/64" 0.4219 10.7156 7/16" 0.4375 11.1125 7/16" 0.4375 11.1125
3/8" 18 9/16" 0.5625 14.2875 37/64" 0.5781 14.6844 19/32" 0.5938 15.0813
1/2" 14 11/16" 0.6875 17.4625 45/64" 0.7031 17.8594 23/32" 0.7188 18.2563
3/4" 14 57/64" 0.8906 22.6219 29/32" 0.9063 23.0188 15/16" 0.9375 23.8125
1" 11.5 1-1/8" 1.125 28.575 1-9/32" 1.2813 32.5438 1-5/32" 1.1563 29.3688
1-1/4" 11.5 1-15/32" 1.4688 37.3063 1-31/64" 1.4844 37.7031 1-1/2" 1.5 38.1
1-1/2" 11.5 1-23/32" 1.7188 43.6563 1-23/32" 1.7188 43.6563 1-3/4" 1.75 44.45
2" 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" 8 2-25/32" 2.7813 70.6438 2-5/8" 2.625 66.675 2-5/8" 2.625 66.675
3" 8 3-9/32" 3.2813 83.3438 3-1/4" 3.25 82.55 3-1/4" 3.25 82.55
3-1/2" 8 3-3/4" 3.75 95.25 3-3/4" 3.75 95.25 3-3/4" 3.75 95.25
4" 8 4-1/4" 4.25 107.95 4-1/4" 4.25 107.95 4-1/4" 4.25 107.95
5" 8 5-1/4" 5.25 133.35 5-9/32" 5.2813 134.1438 5-5/16" 5.3125 134.9375
6" 8 6-1/4" 6.25 158.75 6-11/32" 6.3438 161.1313 6-3/8" 6.375 161.925

Notes:
* 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.
Tolerances:
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)

Note- 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


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