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Technical Information
Taper Pipe Tap Thread Limits • Ground Thread • Reference USCTI Table 338
American National Standard Taper Pipe Thread Form (NPT)
Aeronautical National Taper Pipe Thread Form (ANPT)
Dryseal American National Standard Taper Pipe Thread Form (NPTF)
Projection*
taper per foot limits
nominal
size
(in) threads
per inch
1/16 projection*
(in) projection
tolerance
+ / – min max length L1 tap drill size**
NPT, ANPT, NFTF
27 .312 .063 .719 .781 .160 C
1/8 27 .312 .063 .719 .781 .1615 Q
1/4 18 .459 .063 .719 .781 .2278 7/16
3/8 18 .454 .063 .719 .781 .240 9/16
1/2 14 .579 .063 .719 .781 .320 45/64
3/4 14 .565 .063 .719 .781 .339 29/32
1 11-1/2 .678 .094 .719 .781 .400 1-9/64
1-1/4 11-1/2 .686 .094 .719 .781 .420 1-31/64
1-1/2 11-1/2 .699 .094 .719 .781 .420 1-23/32
2 11-1/2 .667 .094 .719 .781 .436 2-3/16
2-1/2 8 .925 .094 .734 .781 .682 2-39/64
3 8 .925 .094 .734 .781 .766 3-15/64
3-1/2 8 .938 .125 .734 .781 .821 —
4 8 .950 .125 .734 .781 .844 —
*Distance from small end of tap projects through L1 taper thread ring gage.
**Recommended size given permits direct tapping without reaming the hole, but only gives a full thread for approximately the L1 length.
Reprinted with permission from United States Cutting Tool Institute (USCTI). Published by Kennametal Inc. © 2014. All rights reserved.
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Pipe Taps
Short projection pipe taps are made with a
projection shorter than standard for taper pipe
tapping where the depth of tapping is limited.
Ground thread pipe taps are standard in
American Standard Pipe Form (NPT) and
American Standard Dryseal Pipe Form (NPFT).
NPT threads require the use of a sealer, like
Teflon ® tape or pipe compound. Dryseal taps are
used to tap fittings, which will give a pressure-
tight joint without the use of a sealer.
The nominal size of a pipe tap is that of the pipe
fitting to be tapped, not the actual size of the
tap. The thread tapers 3/4" per foot.
Standard
Projection
L1
Ring Gage
Shortest
Projection
Basic
Size
Special short projection taper pipe taps can
be furnished with American National Standard
Taper Pipe thread (ANPT) or Dryseal American
National Standard Taper Pipe thread (NPTF,
PTF-SAE Short, or PTF-SPL Extra Short).
For information on short projection pipe taps
and hole preparation for NPT, NPTF, and ANPT
internal pipe threads, consult WIDIA-GTD ™
Technical Bulletins.
All pipe taps are furnished with 2-1/2–3-1/2
thread chamfer.
widia.com
Y93
General-purpose pipe taps are appropriate for
threading a wide variety of materials, both ferrous
and non-ferrous.