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TAPER PIPE THREAD GAGES
METHOD OF GAGING PRODUCT
METHOD OF GAGING PRODUCT NPT
ANPT AND NPTF
Internal Threads. The internal thread is first
Internal Taper Pipe Threads: The plug gage is
gaged with a limit-type L1 taper thread plug gage,
screwed up tight by hand into the internal thread of
and the gaging notch which most nearly
the product. The thread is within the permissible
represents the size of the thread is noted.
tolerance when the gaging notch of the working
plug is not more than plus or minus one turn from
MINIMUM
being flush with the end of the thread. Fig. 1.
FLUSH
ONE TURN LARGE
ONE TURN SMALL
B
MAXIMUM
BASIC
MAXIMUM
MINIMUM
Fig. 5 Checking fitting with L3 thread Plug Gages.
Fig. 1 Gaging internal American National Taper pipe
The three product threads beyond the L1 are called
threads with working gage. When the internal thread
is chambered, the gaging point shall be the intersec-
the L3 length and are the additional threads which
tion of the chamber and the pitch cone of the thread.
will be engaged when the pipe is tightened with a
wrench, or "wrench tight". These threads are next
External Taper Pipe Threads: In gaging external
gaged with an L3 taper thread plug gage. This is
taper threads, the ring gage is screwed up tight by
hand on the external thread of the product. The
also a limit type gage with the length equal to L1
thread is within the permissible tolerance when the
plus L3, but which
the gaging face of the working ring is plus or minus
has four threads at
MINt
one turn from being flush with the end of the
the small end only.
B
thread. Figure 2.
For a thread to be
Bt
acceptable on an
L3 gage, the posi-
tion of the gaging Fig. 6 Checking minor diameter
ONE TURN LARGE
ONE TURN SMALL
FLUSH
truncation with 6 step plain
notch must coincide
Plug Gages.
within 1/2 turn of the
position previously noted on the L1 gage. The L1
and the L3 together check the lead, taper, pitch
diameter, and the major diameter.
The minor diameter of internal threads is
BASIC
MAXIMUM
MINIMUM
Fig. 2 Gaging external NPT threads.
determined by the amount of truncation of the
thread crests. As the truncation and pitch diameter
varies within limits, so will the minor diameter vary
Limit Type Plug and Ring Gages
and for this reason it is customary to refer to minor
diameter as at "maximum truncation" or "minimum
The limit type gage is used to eliminate counting
truncation". There are also 3 pitch diameter gaging
turns by which the gage over or under travels to the
positions: basic,minimum, and maximum which
basic surface.
necessitates 3 pairs of maximum and minimum
MINIMUM
truncation steps, or a total of 6 positions.
MINIMUM
To gage the minor diameter, a 6 step plain plug
B
gage is always used in connection with the L1
gage. The L1 gage is used as a guide to determine
BASIC
the gaging position. If the basic gage notch is flush
MAXIMUM
MAXIMUM
with end of the product, the threads are
Fig. 4
Fig. 3
considered to be basic. The plain plug gage used
L2 limit type Ring Gage
L1 limit type Plug Gage
on the same fitting should show the end of the
product at or between the basic
The gages include the basic notch on the plug and
maximum and minimum notches.
the basic surface on the ring and in addition include
two notches, or steps, on both plug and ring. One
External Threads: ANPT and
notch is considered the maximum and the other the
NPTF external threads are first
minimum. The retention of the basic step, or notch,
gaged with a thin L1 taper thread
facilitates checking against master and reference
ring gage. Observe the small end
gages and provides a means of checking the max-
of the gaging face of the ring to the
imum and minimum steps.
small end of the pipe.
Fig. 7 L2 Thick
Ring Gage
12
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TAPER PIPE THREAD GAGES
MAXIMUM
The L2 ring is used to gage the effective external
The 6 step plain taper ring gage checks the truncation
threads beyond the L1 location length. It is relieved
of the crest at the major diameter. Three of the steps
MINIMUM
by counterboring at the small end to a depth equal
represent the minimum truncation for the basic,
to L1 minus 1P. The L2 is used like the thin L1 gage
maximum and minimum thread sizes B, MN, MX.
is used with a count of the number of turns by which
The other three represent the corresponding
the product over travels or fails to reach basic. The
maximum truncation.
BASIC
two gages together inspect the lead, pitch diameter,
taper, and minor diameter. When both the L1 and L2
The 6 step plain ring is used similar to the 6 step plain
Fig. 8 Checking major
rings are used, the relative position of the small end
plug. The ring is always used with a limit type thin L1
diameter truncation with
of the pipe and the basic gaging face of the rings
ring gage.
6 step plain ring gage.
may not vary more than 1/2 turn.
TAPER PIPE THREAD GAGES - NPT AND NPTF
NPT(ANSI/ASME B1.20.1)
NPTF(ANSI/ASME B1.20.5)
SIZE
NPT
NPT
NPTF
NPTF
NPTF
NPTF
NPTF
Plug
Ring
Plugs L1 Plugs 6 Rings L1 Rings L2 Rings 6
or L3 step plain
step plain
HANDLES
1/16-27
$65.00
$126.00
$81.00
$131.00
$133.00
$186.00
$208.00
$9.00
1/8-27
47.00
88.00
60.00
131.00
92.00
180.00
208.00
9.00
1/4-18
53.00
96.00
69.00
131.00 110.00
186.00
208.00
9.00
131.00 115.00
181.00
208.00
10.00
3/8-18
59.00
103.00
82.00
1/2-14
66.00
115.00
95.00
131.00 121.00
188.00
208.00
10.00
3/4-14
76.00
130.00 104.00
139.00 134.00
208.00
233.00
10.00
1.0-111/2
85.00
143.00 115.00
150.00 157.00
227.00
233.00
10.00
11/4-111/2
95.00
163.00 125.00
160.00 166.00
246.00
254.00
10.00
11/2-111/2
107.00
194.00 140.00
175.00 200.00
270.00
291.00
10.00
2.0-111/2
130.00
232.00 170.00
243.00 283.00
312.00
325.00
10.00
21/2-8
157.00
272.00 250.00
374.00 307.00
374.00
386.00
13.00
3.0-8
182.00
355.00 280.00
405.00 348.00
442.00
472.00
13.00
31/2-8
280.00
450.00
Priced on Request
15.00
4-8
305.00
515.00
Priced on Request
15.00
5-8
405.00
615.00
Priced on Request
15.00
6-8
505.00
725.00
Priced on Request
15.00
Master gages priced on request.
Long form calibration - add $25. per gage.
TAPER PIPE THREADS - ANPT - WORKING & INSPECTION
L-1
L-2
Plain
L-1
L-3
Plain
Size
Ring Gage Ring Gage
Taper
Plug Gage Plug Gage
Taper
Handle
Basic
Basic
Ring
Basic
Basic
Plug
Step
Step
6 Step
Step
Step
6 Step
1/16-27
$149.00
$206.00
$229.00
$118.00
$121.00
$148.00
$8.00
1/8-27
135.00
200.00
229.00
91.00
94.00
148.00
8.00
1/4-18
125.00
206.00
229.00
103.00
108.00
148.00
8.00
3/8-18
123.00
201.00
229.00
121.00
122.00
148.00
8.00
1/2-14
136.00
209.00
229.00
131.00
135.00
148.00
9.00
3/4-14
151.00
229.00
254.00
141.00
146.00
155.00
9.00
1.0-111/2
174.00
249.00
254.00
153.00
158.00
169.00
10.00
11/4-111/2
184.00
268.00
277.00
166.00
166.00
178.00
10.00
11/2-111/2
220.00
298.00
316.00
185.00
185.00
193.00
10.00
2.0-111/2
315.00
350.00
352.00
214.00
214.00
265.00
10.00
21/2-8
340.00
410.00
416.00
321.00
321.00
402.00
14.00
3.0-8
390.00
490.00
505.00
358.00
358.00
435.00
14.00
Long form calibration - add $25. per gage.
13
Thread Check,Tel:631-231-1515 Fax:631-231-1625 Toll-Free:Tel:800-767-7633 Fax:800-767-2034 www.threadcheck.com Email: info@threadcheck.com