3 1/2-8 NPSH NPSH (pipe-size hose) Internal Thread Specifications
3 1/2-8NPSH INT
ASMESTD: ASME B1.20.7SOURCE: Table 3 · p. 6TYPE: Internal (nut/tapped hole)CLASS: StdSERIES: NPSH (pipe-size hose)
Major diameter
4.0111 – 3.9820
max – min
Pitch diameter
3.9119 – 3.9008
max – min
Minor diameter
3.8418 – 3.8196
max – min
Pitch
0.12500
8 threads per inch
Thread profile
3 1/2-8NPSH INT: solid line = maximum material profile, dashed = minimum material, hatched = tolerance zone, grey dashed = basic profile. Drawn to scale; values in inches, diameters shortened.
Limits of size, class Std
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter DPara. 3.1: tolerance = 2 × PD tolerance | 3.9820 | 4.0111ref. | 3.9820 | 0.0291ref. |
| Pitch diameter D2 | 3.9008 | 3.9119 | 3.9008 | 0.0111 |
| Minor diameter D1 | 3.8196 | 3.8418 | 3.8196 | 0.0222 |
| Allowance es | — |
Dimensions in inches. Values are those of the standard (ASME B1.20.7); calculated cells follow the standard’s formulas. Where the standard prints a value that differs from its formula, the printed value is shown with a note.
Tolerance zones relative to the basic size, inches
Mating, gaging and dimensions
Mating member and fit at the limits
- Service
- Steam, air, water, and all other hose connections to be made up with standard pipe threads
- Mating group (compatible designations)
- NPSH-3_1/2
- Mating member of the same designation
- 3 1/2-8NPSH EXT
- Other designations in the mating group
- none (mates only with its own designation)
- Minimum PD clearance (coupling min − nipple max)
- 0.0120 in
- Maximum PD clearance (coupling max − nipple min)
- 0.0342 in
- Minimum major dia clearance
- 0.0120 in
- Minimum minor dia clearance
- 0.0120 in
- Fit at the limits (PD)
- clearance (always)
Lead, flank and profile
- Lead variation ± (Table 5) ±δP
- 0.0032 in
- Half-angle variation ± (Table 5) ±δα
- 1° 42′
- Lead angle at the basic PD λ
- 0° 35′
- Crest flat (basic P/8)
- 0.015625 in
- Root flat (basic P/8)
- 0.015625 in
- Extreme flat P/24 at minimum PD
- 0.005208 in
- Root radius for the model (worn tool) r
- 0.013532 in
Table 4 dimensions (nipple and coupling)
- As printed
- H 1 1/16; T 13/16; n 6 1/2
- Depth of the coupling H
- 1.06250 in
- Thread length of the coupling T
- 0.81250 in
Setting plugs (Table 8) and plug gages (Table 7)
- Plug gage GO major max / min
- 3.9827 / 3.9820 in
- Plug gage GO pitch max / min
- 3.9013 / 3.9008 in
- Plug gage NOT GO pitch max / min
- 3.9119 / 3.9114 in
Notes
- Maximum major diameter, major diameter tolerance (internal) are reference values from para. 3.2; root radius and stress area are not given in the standard.
Mates
3 1/2-8NPSH INT takes a thread of the same standard at the same size and pitch. The standard mating external thread is class Std. Check the fit with the standard pair →
Working out the mating options…
Different pitch or a different thread family never mate; the fit check runs over both tolerance zones.
Related thread sizes
Same diameter other pitch, and neighbouring sizes
All values for 3 1/2-8NPSH INTevery column of the workbook row
| Designation | 3 1/2-8NPSH INT |
|---|---|
| Decimal / alternate designation | 3.5000-8NPSH INT |
| Threads per inch | 8 |
| Thread form | NPSH |
| Series | NPSH |
| Series name | Hose to pipe thread (NPSH) |
| External / internal | Internal |
| Class | Std |
| Nominal size of hose | 3 1/2 |
| Pitch P (in.) | 0.12500 |
| Basic major dia D (in.) | 3.9820 |
| Size category | Standard sizes (Tables 1-8) |
| Source table | Table 3 |
| Printed page | 6 |
| Major dia max (in.) | 4.0111 |
| Major dia min (in.) | 3.9820 |
| Major dia tolerance (in.) | 0.0291 |
| Basic pitch dia D2 (in.) | 3.9008 |
| Pitch dia max (in.) | 3.9119 |
| Pitch dia min (in.) | 3.9008 |
| PD tolerance (in.) | 0.0111 |
| Basic minor dia D1 (in.) | 3.8196 |
| Minor dia max (in.) | 3.8418 |
| Minor dia min (in.) | 3.8196 |
| Minor dia tolerance (in.) | 0.0222 |
| Major dia status | Minimum printed; maximum is a reference value (para. 3.2: PD max + 11h/9) |
| Minor dia status | Toleranced (para. 3.2: tolerance = 2 x PD tolerance) |
| Root radius max (in.) | not given in the standard |
| Root radius min (in.) | not given in the standard |
| Lead variation ± (in.) (Table 5) | 0.0032 |
| Half-angle variation ± (Table 5) | 1° 42′ |
| Lead variation from PD tol (calc) (in.) | 0.0032 |
| Half-angle variation from PD tol (calc) | 1° 42′ |
| Lead angle at basic PD (deg) | 0.5844 |
| Lead angle (deg min) | 0° 35′ |
| Tensile stress area As (sq in.) | not given in the standard |
| Thread angle (deg) | 60 |
| Flank angle (deg) | 30 |
| Sharp V height H (in.) | 0.108253 |
| Thread height h (in.) | 0.081190 |
| Crest flat, basic P/8 (in.) | 0.015625 |
| Root flat, basic P/8 (in.) | 0.015625 |
| Extreme flat P/24 at minimum PD (in.) | 0.005208 |
| Truncation of the P/8 flat from the sharp V, f = h/6 (in.) | 0.013532 |
| Root radius for model (worn tool) (in.) | 0.013532 |
| Sweep cut: start diameter (in.) | 3.819600 |
| Sweep cut: tip diameter (in.) | 3.982000 |
| Sweep cut: depth (in.) | 0.081200 |
| Sweep cut: profile width at start diameter (in.) | 0.109387 |
| Crest flat as modelled (in.) | 0.015613 |
| Taper | none (straight thread) |
| Service | Steam, air, water, and all other hose connections to be made up with standard pipe threads |
| Mating group (compatible designations) | NPSH-3_1/2 |
| Mating member of the same designation | 3 1/2-8NPSH EXT |
| Other designations in the mating group | none (mates only with its own designation) |
| Min PD clearance: coupling min PD - nipple max PD (in.) | 0.0120 |
| Max PD clearance: coupling max PD - nipple min PD (in.) | 0.0342 |
| Min major dia clearance: coupling min - nipple max (in.) | 0.0120 |
| Min minor dia clearance: coupling min - nipple max (in.) | 0.0120 |
| Fit at the limits (PD) | clearance (always) |
| Table 4 lengths as printed | H 1 1/16; T 13/16; n 6 1/2 |
| Table 4: H depth of coupling (in.) | 1.06250 |
| Table 4: T thread length of coupling (in.) | 0.81250 |
| Table 4: approx number of threads in T | 6.50000 |
| Table 7 plug gage: GO major max (in.) | 3.9827 |
| Table 7 plug gage: GO major min (in.) | 3.9820 |
| Table 7 plug gage: GO pitch max (in.) | 3.9013 |
| Table 7 plug gage: GO pitch min (in.) | 3.9008 |
| Table 7 plug gage: NOT GO major max (in.) | 3.9660 |
| Table 7 plug gage: NOT GO major min (in.) | 3.9653 |
| Table 7 plug gage: NOT GO pitch max (in.) | 3.9119 |
| Table 7 plug gage: NOT GO pitch min (in.) | 3.9114 |
| Table 7 plug gage: Z GO minor max (in.) | 3.81980 |
| Table 7 plug gage: Z GO minor min (in.) | 3.81960 |
| Table 7 plug gage: Z NOT GO minor max (in.) | 3.84180 |
| Table 7 plug gage: Z NOT GO minor min (in.) | 3.84160 |
| Check against formulas | OK |
| Notes | Maximum major diameter, major diameter tolerance (internal) are reference values from para. 3.2; root radius and stress area are not given in the standard. |
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ASME B1.20.7: Hose Coupling Screw Threads, Inch. Source: workbook data (2026-10-10). Confirm against your licensed copy of the standard before use.