AMERICAN PIPE THREADS1847 American National Standard pipe threads described in the following paragraphs provide taper and straight pipe threads for use in various combinations and with certain modifica- tions to meet these specific needs. American National Standard Taper Pipe Threads.The basic dimensions of the ANSI Standard taper pipe thread are given in Table 4. Form of Thread: The angle between the sides of the thread is 60 degrees when measured in an axial plane, and the line bisecting this angle is perpendicular to the axis. The depth of the truncated thread is based on factors entering into the manufacture of cutting tools and the making of tight joints and is given by the formulas in Table 4 or the data in Table 1 obtained from these formulas. Although the standard shows flat surfaces at the crest and root of the thread, some rounding may occur in commercial practice, and it is intended that the pipe threads of product shall be acceptable when crest and root of the tools or chasers lie within the limits shown in Table 1. Table 1. Limits on Crest and Root of American National Standard External and Internal Taper Pipe Threads, NPT ANSI/ASME B1.20.1-1983 (R1992) 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. Pitch Diameter Formulas: In the following formulas, which apply to the ANSI Standard taper pipe thread, E0 = pitch diameter at end of pipe; E1 = pitch diameter at the large end of the internal thread and at the gaging notch; D = outside diameter of pipe; L1 = length of hand-tight or normal engagement between external and internal threads; L2 = basic length of effective external taper thread; and p = pitch = 1 number of threads per inch. Thread Length: The formula for L2 determines the length of the effective thread and includes approximately two usable threads that are slightly imperfect at the crest. The nor- INTERNAL THREAD EXTERNAL THREAD Threads per Inch Height of Sharp V Thread, H Height of Pipe Thread, h Truncation, f Width of Flat, F, Equivalent toTruncation Max.Min.Min.Max.Min.Max. 270.032080.029630.024960.00120.00360.00140.0041 180.048110.044440.038330.00180.00490.00210.0057 140.061860.057140.050710.00240.00560.00270.0064 1112 0.075310.069570.062610.00290.00630.00330.0073 80.108250.100000.092750.00410.00780.00480.0090 Max.h H Crest Root Root Crest Crest Maximum Truncation Minimum TruncationMinimum Truncation Maximum Truncation Maximum Truncation Maximum Truncation Minimum Truncation Minimum Truncation E0D0.05D1.1+()p= E1E00.0625L1+= 1848AMERICAN PIPE THREADS mal length of engagement, L1, between external and internal taper threads, when assem- bled by hand, is controlled by the use of the gages. Taper: The taper of the thread is 1 in 16, or 0.75 inch per foot, measured on the diameter and along the axis. The corresponding half-angle of taper or angle with the center line is 1 degree, 47 minutes. Tolerances on Thread Elements.The maximum allowable variation in the commer- cial product (manufacturing tolerance) is one turn large or small from the basic dimen- sions. The permissible variations in thread elements on steel products and all pipe made of steel, wrought iron, or brass, exclusive of butt-weld pipe, are given in Table 2. This table is 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 B1.20.1 will pro- vide 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. Tolerances on Taper, Lead, and Angle of Pipe Threads of Steel Products and All Pipe of Steel, Wrought Iron, or Brass ANSI B1.20-1983 (R1992) (Exclusive of Butt-Weld Pipe) For tolerances on height of thread, see Table 1. 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. Table 3. Internal Threads in Pipe Couplings, NPSC for Pressuretight Joints with Lubricant or Sealer ANSI/ASME B1.20.1-1983 (R1992) Nominal Pipe Size Threads per Inch Taper on Pitch Line (34 in./ft)Lead in Length of Effective Threads 60 Degree Angle of Threads, DegreesMax.Min. 116, 18 27+181160.003 212 14, 38 18 +18116 0.0032 12, 34 14 +181160.003a 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. 2 1, 114, 112, 21112+181160.003a112 212 and larger8+181160.003a112