2.5-7.5 NH-FIRE NH fire hose (App. A) External Thread Specifications
2.5-7.5 NH EXT
ASMESTD: ASME B1.20.7SOURCE: Table A3 · p. 14TYPE: External (bolt/screw)CLASS: StdSERIES: NH fire hose (App. A)
Major diameter
3.0686 – 3.0366
max – min
Pitch diameter
2.9820 – 2.9660
max – min
Minor diameter
2.8954 – 2.8602
max – min
Pitch
0.13333
7.5 threads per inch
Thread profile
2.5-7.5 NH EXT: 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 | 3.0836 | 3.0686 | 3.0366 | 0.0320 |
| Pitch diameter d2 | 2.9970 | 2.9820 | 2.9660 | 0.0160 |
| Minor diameter d1Max printed; min is a reference value | 2.9104 | 2.8954 | 2.8602ref. | 0.0352ref. |
| Allowance es | 0.0150 |
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
- Fire hose coupling (Appendix A, for information only)
- Mating group (compatible designations)
- FH-2.5-7.5_NH
- Mating member of the same designation
- 2.5-7.5 NH INT
- Other designations in the mating group
- none (mates only with its own designation)
- Minimum PD clearance (coupling min − nipple max)
- 0.0150 in
- Maximum PD clearance (coupling max − nipple min)
- 0.0470 in
- Minimum major dia clearance
- 0.0150 in
- Minimum minor dia clearance
- 0.0150 in
- Fit at the limits (PD)
- clearance (always)
Lead, flank and profile
- Lead variation ± (Table 5) ±δP
- not given in the standard in
- Half-angle variation ± (Table 5) ±δα
- not given in the standard
- Lead angle at the basic PD λ
- 0° 49′
- Crest flat (basic P/8)
- 0.016667 in
- Root flat (basic P/8)
- 0.016667 in
- Extreme flat P/24 at minimum PD
- 0.005556 in
- Root radius for the model (worn tool) r
- 0.014434 in
Table 4 dimensions (nipple and coupling)
- As printed
- not given in the standard
- Inside diameter of the nipple C
- not given in the standard in
- Approximate OD of the external thread OD
- not given in the standard in
- Length of the nipple L
- not given in the standard in
- Pilot length l
- not given in the standard in
- Depth of the coupling H
- not given in the standard in
- Thread length of the coupling T
- not given in the standard in
Ring gages (Table 6)
- GO pitch max / min
- not given in the standard / not given in the standard in
- GO minor max / min
- not given in the standard / not given in the standard in
- NOT GO pitch max / min
- not given in the standard / not given in the standard in
- NOT GO minor max / min
- not given in the standard / not given in the standard in
- Z GO major max / min
- not given in the standard / not given in the standard in
- Z NOT GO major max / min
- not given in the standard / not given in the standard in
Setting plugs (Table 8) and plug gages (Table 7)
- GO truncated major max / min
- not given in the standard / not given in the standard in
- GO full major max / min
- not given in the standard / not given in the standard in
- GO pitch max / min
- not given in the standard / not given in the standard in
- NOT GO truncated major max / min
- not given in the standard / not given in the standard in
- NOT GO pitch max / min
- not given in the standard / not given in the standard in
- Plug gage GO major max / min
- not given in the standard / not given in the standard in
- Plug gage GO pitch max / min
- not given in the standard / not given in the standard in
- Plug gage NOT GO pitch max / min
- not given in the standard / not given in the standard in
Notes
- Appendix A is for information only (not part of the standard). Tables 4 to 8 (lengths, lead and half-angle, gages) are not given for fire hose sizes. Root radius and tensile stress area are not given in the standard.
Mates
2.5-7.5 NH EXT screws into a thread of the same standard at the same size and pitch. The standard mating internal 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 2.5-7.5 NH EXTevery column of the workbook row
| Designation | 2.5-7.5 NH EXT |
|---|---|
| Decimal / alternate designation | 2 1/2-7.5 NH EXT |
| Threads per inch | 7.5 |
| Thread form | NH |
| Series | FH |
| Series name | Fire hose (Appendix A, information only) |
| External / internal | External |
| Class | Std |
| Nominal size of hose | 2 1/2 |
| Pitch P (in.) | 0.13333 |
| Basic major dia D (in.) | 3.0836 |
| Size category | Appendix A (information only) |
| Source table | Table A3 |
| Printed page | 14 |
| Major dia max (in.) | 3.0686 |
| Major dia min (in.) | 3.0366 |
| Major dia tolerance (in.) | 0.0320 |
| Allowance es (in.) | 0.0150 |
| Basic pitch dia D2 (in.) | 2.9970 |
| Pitch dia max (in.) | 2.9820 |
| Pitch dia min (in.) | 2.9660 |
| PD tolerance (in.) | 0.0160 |
| Basic minor dia D1 (in.) | 2.9104 |
| Minor dia max (in.) | 2.8954 |
| Minor dia min (in.) | 2.8602 |
| Minor dia tolerance (in.) | 0.0352 |
| Major dia status | Toleranced (para. 3.1: tolerance = 2 x PD tolerance) |
| Minor dia status | Maximum printed; minimum is a reference value (para. 3.1: P/24 flat at min PD) |
| Root radius max (in.) | not given in the standard |
| Root radius min (in.) | not given in the standard |
| Lead variation ± (in.) (Table 5) | not given in the standard |
| Half-angle variation ± (Table 5) | not given in the standard |
| Lead variation from PD tol (calc) (in.) | not given in the standard |
| Half-angle variation from PD tol (calc) | not given in the standard |
| Lead angle at basic PD (deg) | 0.8113 |
| Lead angle (deg min) | 0° 49′ |
| Tensile stress area As (sq in.) | not given in the standard |
| Thread angle (deg) | 60 |
| Flank angle (deg) | 30 |
| Sharp V height H (in.) | 0.115470 |
| Thread height h (in.) | 0.086603 |
| Crest flat, basic P/8 (in.) | 0.016667 |
| Root flat, basic P/8 (in.) | 0.016667 |
| Extreme flat P/24 at minimum PD (in.) | 0.005556 |
| Truncation of the P/8 flat from the sharp V, f = h/6 (in.) | 0.014434 |
| Root radius for model (worn tool) (in.) | 0.014434 |
| Sweep cut: start diameter (in.) | 3.068600 |
| Sweep cut: tip diameter (in.) | 2.895400 |
| Sweep cut: depth (in.) | 0.086600 |
| Sweep cut: profile width at start diameter (in.) | 0.116664 |
| Crest flat as modelled (in.) | 0.016669 |
| Taper | none (straight thread) |
| Service | Fire hose coupling (Appendix A, for information only) |
| Mating group (compatible designations) | FH-2.5-7.5_NH |
| Mating member of the same designation | 2.5-7.5 NH INT |
| Other designations in the mating group | none (mates only with its own designation) |
| Min PD clearance: coupling min PD - nipple max PD (in.) | 0.0150 |
| Max PD clearance: coupling max PD - nipple min PD (in.) | 0.0470 |
| Min major dia clearance: coupling min - nipple max (in.) | 0.0150 |
| Min minor dia clearance: coupling min - nipple max (in.) | 0.0150 |
| Fit at the limits (PD) | clearance (always) |
| Table 4 lengths as printed | not given in the standard |
| Table 4: C inside dia of nipple (in.) | not given in the standard |
| Table 4: approx OD of external thread (in.) | not given in the standard |
| Table 4: L length of nipple (in.) | not given in the standard |
| Table 4: l pilot length (in.) | not given in the standard |
| Table 4: H depth of coupling (in.) | not given in the standard |
| Table 4: T thread length of coupling (in.) | not given in the standard |
| Table 4: approx number of threads in T | not given in the standard |
| Table 6 ring gage: GO pitch max (in.) | not given in the standard |
| Table 6 ring gage: GO pitch min (in.) | not given in the standard |
| Table 6 ring gage: GO minor max (in.) | not given in the standard |
| Table 6 ring gage: GO minor min (in.) | not given in the standard |
| Table 6 ring gage: NOT GO pitch max (in.) | not given in the standard |
| Table 6 ring gage: NOT GO pitch min (in.) | not given in the standard |
| Table 6 ring gage: NOT GO minor max (in.) | not given in the standard |
| Table 6 ring gage: NOT GO minor min (in.) | not given in the standard |
| Table 6 ring gage: Z GO major max (in.) | not given in the standard |
| Table 6 ring gage: Z GO major min (in.) | not given in the standard |
| Table 6 ring gage: Z NOT GO major max (in.) | not given in the standard |
| Table 6 ring gage: Z NOT GO major min (in.) | not given in the standard |
| Table 8 setting plug: GO truncated major max (in.) | not given in the standard |
| Table 8 setting plug: GO truncated major min (in.) | not given in the standard |
| Table 8 setting plug: GO full major max (in.) | not given in the standard |
| Table 8 setting plug: GO full major min (in.) | not given in the standard |
| Table 8 setting plug: GO pitch max (in.) | not given in the standard |
| Table 8 setting plug: GO pitch min (in.) | not given in the standard |
| Table 8 setting plug: NOT GO truncated major max (in.) | not given in the standard |
| Table 8 setting plug: NOT GO truncated major min (in.) | not given in the standard |
| Table 8 setting plug: NOT GO full major max (in.) | not given in the standard |
| Table 8 setting plug: NOT GO full major min (in.) | not given in the standard |
| Table 8 setting plug: NOT GO pitch max (in.) | not given in the standard |
| Table 8 setting plug: NOT GO pitch min (in.) | not given in the standard |
| Table 8 setting plug: Full-form GO major max (in.) | not given in the standard |
| Table 8 setting plug: Full-form GO major min (in.) | not given in the standard |
| Table 8 setting plug: Full-form NOT GO major max (in.) | not given in the standard |
| Table 8 setting plug: Full-form NOT GO major min (in.) | not given in the standard |
| Table 7 plug gage: GO major max (in.) | not given in the standard |
| Table 7 plug gage: GO major min (in.) | not given in the standard |
| Table 7 plug gage: GO pitch max (in.) | not given in the standard |
| Table 7 plug gage: GO pitch min (in.) | not given in the standard |
| Table 7 plug gage: NOT GO major max (in.) | not given in the standard |
| Table 7 plug gage: NOT GO major min (in.) | not given in the standard |
| Table 7 plug gage: NOT GO pitch max (in.) | not given in the standard |
| Table 7 plug gage: NOT GO pitch min (in.) | not given in the standard |
| Table 7 plug gage: Z GO minor max (in.) | not given in the standard |
| Table 7 plug gage: Z GO minor min (in.) | not given in the standard |
| Table 7 plug gage: Z NOT GO minor max (in.) | not given in the standard |
| Table 7 plug gage: Z NOT GO minor min (in.) | not given in the standard |
| Check against formulas | OK |
| Notes | Appendix A is for information only (not part of the standard). Tables 4 to 8 (lengths, lead and half-angle, gages) are not given for fire hose sizes. Root radius and tensile 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.