Pipe Thread data sheet


External (pipe) Basic Thread Dimensions

For interpertations of the terms scroll down to the drawings below the table

Property Inch mm
Nominal Pipe Size (Ø) 1/4" ...
Pipe Outside Diameter (D) 0.54 13.716
Pitch (TPI) (P) 18.000 457.2
Pitch (Distance) (P) 0.05555556 1.411
Thread Tapper Angle (ß) 1.7893° 1.7893°
Thread V half Angle (α) 30° 30°
Height of sharp V (H) 0.048113 1.222
Thread height (h) 0.04444 1.129
Pitch Diameter at the Pipe's end (E0) 0.47739 12.126
Minor Diameter at the Pipe's end (K0) 0.4329 10.996
Hand-Tight Engagement Length (L1) 0.2278 5.786
Pitch Diameter at L1 plane (E1) 0.49163 12.487
Length of Last Complete Thread (L5) 0.2907 7.384
Pitch Diameter at L5 plane (E5) 0.49556 12.587
Length of Last usefull Thread (L2) 0.4018 10.206
Pitch Diameter at L2 plane (E2) 0.5025 12.764
Overall Thread Length (L4) 0.5946 15.103
Length of Vanish threads (V) 0.1928 4.897

1/4-18 NPT - External (pipe) Drawing

Overview Drawing

Profile Drawing

1/4-18 NPT - Internal (Fitting) Basic Thread Dimensions

For interpertations of the terms scroll down to the drawings below the table

Property Inch mm
Nominal Pipe Size (Ø) 1/4" ...
Pipe Outside Diameter (D) 0.54 13.716
Pitch (TPI) (P) 18.000 457.2
Pitch (Distance) (P) 0.05555556 1.411
Thread Tapper Angle (ß) 1.7893° 1.7893°
Thread V half Angle (α) 30° 30°
Height of sharp V (H) 0.048113 1.222
Thread height (h) 0.04444 1.129
Pitch Diameter at the fitting's end (E1) 0.49163 12.487
Length of Hand-Tight Engagemen (L1) 0.2278 5.786

Length of Wrenching Allowance (L3)

0.1667 4.234
Pitch Diameter at L3 plane (E3) 0.46697 11.861
Tap Drill Size (T) 0.4375 11.113

1/4-18 NPT - Internal (Fitting) Drawing

Overview Drawing

Profile Drawing

1/4-18 NPT - Tolerances

Property Minimum Maximum
Thread Height (h) 0.03833" (0.974 mm) 0.04444" (1.129 mm)
L1 gage Tolerance (+/- 1 Turn) (L1) ... 0.05556" (1.411 mm)
Thread Truncation (f) 0.0018" (0.046 mm) 0.0049" (0.124 mm)
Tapper angle Variation (ß) 1.641" ( ) 2.089" ( )
Thead V Half Angle (+/-) (α) ... 1" ( )
Thread Height (h) " (0 mm) " (0 mm)
L1 gage Tolerance (+/- 1 Turn) (L1) " ( ) " ( )
Thread Truncation (f) " (0 mm) " (0 mm)
Tapper angle Variation (ß) " ( ) " ( )
Thead V Half Angle (+/-) (α) " ( ) " ( )
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