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Pipe Thread Pitch Diameter Formulas and Calculator

Standard ANSI Hardware

Pitch Diameter Formulas and Calculator NPT American National Standard Taper Pipe Threads

Related:

• Basic Dimensions, American National Standard Taper Pipe Threads, NPT
• National Standard Taper Pipe Threads Size NPT Chart - Includes both External and internal Pipe Thread Data

Tapered Pipe Pitch Diameter Calculator Preview

E₀ = D - ( 0.05 D + 1.1 ) p

E₁ = E₀ + 0.0625 L₁

L₂ = (0.80 D + 6.8 ) p

Where:

E_o = pitch diameter at end of pipe;
E₁ = pitch diameter at the large end of the internal thread and at the gaging notch;
L₁ = length of hand-tight or normal engagement between external and internal thread;
L₂ = basic length of effective external taper thread;
D = outside diameter of pipe;
p = pitch = 1 ÷ number of threads per inch.

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.

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 normal length of engagement, L₁, between external and internal taper threads, when assembled 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.

Reference:

ANSI/ASME B1.20.1-1983 (R2006), American National Standard Taper Pipe Threads