Machinery's Handbook, 31st Edition
2092 American Pipe Threads a guide for establishing the limits of the thread elements of taps, dies, and thread chasers. These limits may be required on product threads. On pipe fittings and valves (not steel) for steam pressures 300 pounds and below, it is intended that plug and ring gage practice as set up in the Standard ANSI/ASME B1.20.1- 2013 (R2018) will provide for a satisfactory check of accumulated variations of taper, lead, and angle in such product. Therefore, no tolerances on thread elements have been established for this class. For service conditions where a more exact check is required, procedures have been developed by industry to supplement the regulation plug and ring method of gaging. Table 2. Limits on Crest and Root of American National Standard External and Internal Taper Pipe Threads, NPT ANSI/ASME B1.20.1-2013 (R2018) INTERNAL THREAD
Minimum
Root
Truncation
Minimum
Truncation
Maximum
H
Truncation
Maximum
Minimum
Max. h
Truncation
Truncation
Crest
Crest
Maximum
Truncation
Maximum
Truncation
Root
Minimum
Truncation
EXTERNAL THREAD
Width of Flat, F , Equivalent toTruncation
Height of Pipe Thread, h
Truncation, f
Threads per Inch
Height of Sharp V Thread, H
Max.
Min.
Min.
Max. 0.0036 0.0049 0.0056 0.0063 0.0078
Min.
Max. 0.0041 0.0057 0.0064 0.0073
27 18 14
0.03208 0.04811 0.06186 0.07531 0.10825
0.02963 0.04444 0.05714 0.06957 0.10000
0.02496 0.03833 0.05072 0.06261 0.09275
0.0012 0.0018 0.0024 0.0029 0.0041
0.0014 0.0021 0.0027 0.0033 0.0048
11 1 ∕ 2
8 0.0090 All dimensions are in inches and are given to four or five decimal places only to avoid errors in computations, not to indicate required precision. Table 3. Tolerances on Taper, Lead, and Angle of Pipe Threads of Steel Products and All Pipe of Steel, Wrought Iron, or Brass ANSI/ASME B1.20.1-2013 (R2018) (Exclusive of Butt-Weld Pipe)
Threads per Inch
Lead in Length of Effective Threads
60 Degree Angle of Threads, Degrees
Taper on Pitch Line ( 3 ∕ 4 in/ft)
Nominal Pipe Size
Max.
Min. − 1 ∕ 16 − 1 ∕ 16 − 1 ∕ 16 − 1 ∕ 16 − 1 ∕ 16
27 18 14
1 ∕ 16 , 1 ∕ 8 1 ∕ 4 , 3 ∕ 8 1 ∕ 2 , 3 ∕ 4
± 0.003 ± 0.003 ± 0.003 ± 0.003 ± 0.003
± 2 1 ∕ 2
+ 1 ∕ 8 + 1 ∕ 8 + 1 ∕ 8 + 1 ∕ 8 + 1 ∕ 8
± 2 ± 2
a a a
1, 1 1 ∕ 4 , 1 1 ∕ 2 , 2 2 1 ∕ 2 and larger
11 1 ∕ 2
± 1 1 ∕ ± 1 1 ∕
2
8
2 a The tolerance on lead shall be ±0.003 in. per inch on any size threaded to an effective thread length greater than 1 in. For tolerances on height of thread, see Table 2. The limits specified in this table are intended to serve as a guide for establishing limits of the thread elements of taps, dies, and thread chasers. These limits may be required on product threads.
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