KEVOS® MAKEOS · Threads
NPT Tapped Port Check (Thread Length, Depth, Boss Wall)
Is this tapped NPT pipe port deep enough for a full thread engagement, and is the boss wall around it thick enough?
Check of a tapped port for an NPT tapered pipe thread: pitch diameter at the small end, effective thread length and pitch diameter at that length (as the NPT pipe thread tool), the tapped depth needed for the effective length plus the tap chamfer threads, and the wall left between the thread major diameter and the boss outside diameter, against the depth and wall you have.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Pipe outside diameter | in | Outside diameter of the pipe (e.g. 0.840 in for ½ NPT). |
| Threads per inch | TPI | Threads per inch for the size. |
| Tap chamfer threads to allow | threads | Incomplete threads at the tap end to allow beyond the effective length. |
| Tapped depth available | mm | Depth the boss allows you to tap. |
| Boss outside diameter | mm | Outside diameter of the boss or the narrowest wall across the port. |
| Least wall around the thread | mm | Least wall you accept around the thread for strength and leak tightness. |
Method and formulas
- p = 1 ÷ n; E₀ = D − (0.05D + 1.1)p; L₂ = (0.8D + 6.8)p; E₂ = E₀ + L₂ ÷ 16; thread height 0.8p (as the NPT pipe thread tool).
- Depth needed = L₂ + chamfer threads × p.
- Major diameter near the face ≈ E₂ + 0.8p; wall = (boss − major) ÷ 2.
- Example: tap at least 17.185 mm deep (L₂ = 13.556 mm); the boss leaves 5.2186 mm of wall.
Limitations
- Formula dimensions; hand-tight engagement L₁ and tolerances come from the standard’s tables.
- Wall taken at the effective-length position, which is conservative near the face.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a tapped port in a manifold or casting
- Size a weld-on boss for a pipe thread
- Set the tapping depth on a drawing
Who it is for
- Design engineers
- Machinists
- Hydraulic technicians
What you get
- Small-end pitch diameter, effective length, pitch diameter at L₂
- Tapped depth needed
- Boss wall left
Interpreting the result
- A short port lets the fitting bottom before it seals: tap deep enough for the full effective length.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1952–1975. Topic reference; no source tables or recommended settings are reproduced.
- ASME B1.20.1 Pipe Threads, General Purpose (Inch)
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Open the NPT Tapped Port Check (Thread Length, Depth, Boss Wall) calculator
