1-1/4-11.5 NPSC NPSC (straight, couplings) Internal Thread Specifications
1-1/4-11.5 NPSC · 1.250-11.5 NPSC
ASMESTD: ASME B1.20.1SOURCE: Table 4 · p. 14TYPE: Internal (nut/tapped hole)CLASS: —SERIES: NPSC (straight, couplings)TAPER 1:16
Major diameter
1.6611 – 1.6378
max – min, at the gage plane
Pitch diameter
1.5915 – 1.5752
max – min, at the gage plane
Minor diameter
1.5289 – 1.506
max – min, at the gage plane
Pitch
0.08696
11.5 threads per inch
Thread profile
Internal profile over three pitches at the gage plane, drawn at maximum material (sharpest crest, flattest root); hatched bands are the truncation zones. Diameters shortened.
Thread length, taper and gage planes
Lengths, taper and gage planes to scale; diameters shortened. D and K at the planes are calculated with the mean truncations.
Limits of size, class —
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter D1Root of the internal thread | 1.6611 | 1.6378 | 0.0233 | |
| Pitch diameter E1Straight thread: the limits apply along the whole length | 1.58338 | 1.5915 | 1.5752 | 0.0163 |
| Minor diameter K1Crest of the internal thread | 1.5289 | 1.506 | 0.0229 | |
| Allowance esNone: taper threads are made up to interference (NPT/NPTR); NPSC uses sealant | — | |||
| Crest truncation fcTable 1 (both threads) | 0.006348 | 0.002870 | ||
| Root truncation frTable 1 (both threads) | 0.006348 | 0.002870 | ||
| Crest flat FcEquivalent width of flat | 0.007304 | 0.003304 | ||
| Root flat FrEquivalent width of flat | 0.007304 | 0.003304 |
Dimensions in inches. Values are those of the standard (ASME B1.20.1); 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.
Taper, lengths and gaging
Taper, gage and sealing paras. 3, 5; Tables 1, 3
- Taper on the diameter T
- none (straight)
- Half apex angle of the pitch cone β
- 0 °
- Lead angle at the basic PD λ
- 1° 00′
- Gaging method
- NPT L1 plug gage or L1 internal indicating gage (para. 4.2)
- Gaging tolerance
- ±1-1/2 turns
- Gaging position
- Gaging notch of the NPT L1 plug flush with the face of the coupling
- Sealing
- Pressure-tight with sealant, made up with an NPT external thread (paras. 1.4, 4.1)
NPSC: engagement with an NPT external thread Table 4
- NPT hand-tight at the NPSC PD min, from the small end
- 0.2891 in
- NPT hand-tight at the NPSC PD max, from the small end
- 0.5499 in
L1 plug and ring gages Tables 8 and 9
- Plug gage major dia at the E0 plane
- 1.61505 in
- Plug gage major dia at the gaging notch (E1)
- 1.64130 in
- Plug gage major dia at the large end (E2)
- 1.65922 in
- Gage pitch dia at the E0 plane
- 1.55713 in
- Gage pitch dia at the gaging notch (E1)
- 1.58338 in
- Gage pitch dia at the large end (E2)
- 1.60131 in
- Ring gage minor dia at the E0 plane
- 1.49922 in
- Ring gage minor dia at the gaging notch (E1)
- 1.52547 in
- Thickness of the L1 ring or gage elements
- 0.4200 in
- Working gage crest truncation
- 0.008696 in
- Maximum standoff between plug and ring gages
- 0.047 in
Working gage tolerances Table 7
- On the pitch diameter ±
- 0.0003 in
- Lead, plugs / rings
- 0.0003 / 0.0004 in
- Half angle ±, plugs / rings
- 10 / 15 min
- Taper, plugs / rings
- 0.0008 / 0.0012 in
- Major dia of plugs
- 0.0010 in
- Minor dia of rings
- 0.0010 in
- Total cumulative tolerance on the PD, plugs / rings
- 0.00121 / 0.00170 in
Notes
- Table 4 Note 1: the actual PD of the straight tapped hole will be slightly smaller than the value given when gaged with a taper plug gage (para. 4.2.1). PD sizes correspond to the gaging tolerance of 1-1/2 turns large or small of NPT E1 (para. 4.1.2). Caution (p. 14): when tapered gages are used in straight threads, nonuniformity of gage wear is a particular problem; check the gages directly in addition to checking against a master. NPSC is internal only; the mating external thread is NPT (para. 4.1).
Mates
1-1/4-11.5 NPSC 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 1-1/4-11.5 NPSCevery column of the workbook row
| Designation | 1-1/4-11.5 NPSC |
|---|---|
| Decimal designation | 1.250-11.5 NPSC |
| Threads per inch | 11.5 |
| Thread form | Straight |
| Series | NPSC |
| Series name | Internal Straight Threads in Pipe Couplings |
| External / internal | Internal |
| Class | — |
| Nominal pipe size | 1-1/4 |
| Pitch P (in.) | 0.08695652 |
| O.D. of pipe D, basic major dia (in.) | 1.660 |
| Size category (Table 3 group) | 1, 1-1/4, 1-1/2, 2 (11.5 TPI) |
| Source table | Table 4 |
| Printed page | 14 |
| Where the diameter limits apply | Straight thread: the limits apply along the whole length |
| Major dia max (in.) | 1.6611 |
| Major dia min (in.) | 1.6378 |
| Major dia tolerance (in.) | 0.0233 |
| Major dia status | Calculated: PD limits of Table 4 with Table 1 truncation limits (para. 4.1.2) |
| Basic pitch dia at gage plane E1 (in.) | 1.58338 |
| Pitch dia max (in.) | 1.5915 |
| Pitch dia min (in.) | 1.5752 |
| PD tolerance (in.) | 0.0163 |
| Minor dia max (in.) | 1.5289 |
| Minor dia min (in.) | 1.506 |
| Minor dia tolerance (in.) | 0.0229 |
| Minor dia status | Min printed (Table 4 col. 4); max calculated from PD max and Table 1 truncation |
| Allowance source | None: taper threads are made up to interference (NPT/NPTR); NPSC uses sealant |
| Root radius max (in.) | not given in the standard |
| Root radius min (in.) | not given in the standard |
| Lead / angle / taper source | Not given in the standard for straight threads |
| Lead angle at basic PD (deg) | 1.001487 |
| Lead angle (deg min) | 1° 00′ |
| Tensile stress area As (sq in.) | not given in the standard |
| Thread angle (deg) | 60 |
| Flank angle (deg) | 30 |
| Sharp V height H (in.) | 0.0753066 |
| Thread height h max (in.) | 0.06957 |
| Thread height h min (in.) | 0.06261 |
| Crest truncation min (in.) | 0.002870 |
| Crest truncation max (in.) | 0.006348 |
| Root truncation min (in.) | 0.002870 |
| Root truncation max (in.) | 0.006348 |
| Crest flat min (in.) | 0.003304 |
| Crest flat max (in.) | 0.007304 |
| Root flat min (in.) | 0.003304 |
| Root flat max (in.) | 0.007304 |
| Sweep cut: start diameter (in.) | 1.506 |
| Sweep cut: tip diameter (in.) | 1.64477 |
| Sweep cut: depth (in.) | 0.069385 |
| Sweep cut: profile width at start diameter (in.) | 0.083653 |
| Sweep cut: tip flat (in.) | 0.003304 |
| Sweep cut: start diameter is | Minor dia min (hole); straight |
| Taper half-angle β (deg) | 0 |
| Taper on diameter | none (straight) |
| Gaging method | NPT L1 plug gage or L1 internal indicating gage (para. 4.2) |
| Gaging tolerance (turns) | ±1-1/2 turns |
| Gaging limit large (turns) | 1.5 |
| Gaging limit small (turns) | 1.5 |
| Basic gaging position | Gaging notch of the NPT L1 plug flush with the face of the coupling |
| Sealing | Pressure-tight with sealant, made up with an NPT external thread (paras. 1.4, 4.1) |
| PD min by formula E1 − 1.5 × 0.0625/n | 1.5752 |
| PD max by formula E1 + 1.5 × 0.0625/n | 1.5915 |
| Minor dia min by formula PDmin − (H − 0.066P) | 1.506 |
| NPT external hand-tight at NPSC PD min, from small end (in.) | 0.2891 |
| NPT external hand-tight at NPSC PD max, from small end (in.) | 0.5499 |
| Gage: plug major dia at E0 plane (in.) | 1.61505 |
| Gage: plug major dia at E1 gaging notch (in.) | 1.64130 |
| Gage: plug major dia at E2 large end (in.) | 1.65922 |
| Gage: pitch dia at E0 plane (in.) | 1.55713 |
| Gage: pitch dia at E1 gaging notch (in.) | 1.58338 |
| Gage: pitch dia at E2 large end (in.) | 1.60131 |
| Gage: ring minor dia at E0 plane (in.) | 1.49922 |
| Gage: ring minor dia at E1 gaging notch (in.) | 1.52547 |
| Gage: thickness of L1 ring or gage elements (in.) | 0.4200 |
| Gage: working gage crest truncation (in.) | 0.008696 |
| Gage: root must clear 0.0381P width (in.) | 0.003313 |
| Gage: plug major at E0 by formula E0 + (H − 2·trunc) | 1.61505 |
| Working gage tol. on PD ± (in.) | 0.0003 |
| Working gage tol. lead, plugs (in.) | 0.0003 |
| Working gage tol. lead, rings (in.) | 0.0004 |
| Working gage tol. half angle, plugs ± (min) | 10 |
| Working gage tol. half angle, rings ± (min) | 15 |
| Working gage tol. taper, plugs + (in.) | 0.0008 |
| Working gage tol. taper, rings − (in.) | 0.0012 |
| Working gage tol. major dia, plugs − (in.) | 0.0010 |
| Working gage tol. minor dia, rings + (in.) | 0.0010 |
| Working gage total cumulative tol. on PD, plugs (in.) | 0.00121 |
| Working gage total cumulative tol. on PD, rings (in.) | 0.00170 |
| Max standoff between plug and ring gages (in.) | 0.047 |
| Check against formulas | OK |
| Notes | Table 4 Note 1: the actual PD of the straight tapped hole will be slightly smaller than the value given when gaged with a taper plug gage (para. 4.2.1). PD sizes correspond to the gaging tolerance of 1-1/2 turns large or small of NPT E1 (para. 4.1.2). Caution (p. 14): when tapered gages are used in straight threads, nonuniformity of gage wear is a particular problem; check the gages directly in addition to checking against a master. NPSC is internal only; the mating external thread is NPT (para. 4.1). |
| Lookup key | 1-1/4-11.5 NPSC · Internal |
Related tools
- Thread standardsEvery ISO and ASME thread series and size, with limits and drawings.
- Thread Spec CalculatorDiameters, tolerances and geometry for ISO metric and unified threads.
- Thread Fit CheckPick a bolt and a nut and see the clearance or interference.
- Twist Drill SizesASME B94.11M drills: sizes, lengths, shanks and tolerances.
- Thread Designation GuideHow to read M10×1.5, 1/4-20 UNC-2A, NPT and more.
- Thread Notations & TermsSymbols and terms of a thread profile, explained.
ASME B1.20.1: Pipe Threads, General Purpose, Inch. Source: workbook data (2026-10-11). Confirm against your licensed copy of the standard before use.