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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