3/4-14 NPTR NPTR (taper, railing) External Thread Specifications

3/4-14 NPTR · 0.750-14 NPTR

ASMESTD: ASME B1.20.1SOURCE: Table 5 · p. 15TYPE: External (bolt/screw)CLASS: —SERIES: NPTR (taper, railing)TAPER 1:16
Major diameter
1.04602 – 1.03513
max – min, at the gage plane
Pitch diameter
0.98887 – 0.98441
max – min, at the gage plane
Minor diameter
0.93815 – 0.92727
max – min, at the gage plane
Pitch
0.07143
14 threads per inch

Thread profile

gage plane: hand-tight, L1 from small endthread axisD1 = 1.0460–1.0351major dia (crest)E1 = 0.98887–0.98441pitch dia, basic 0.98887K1 = 0.9382–0.9273minor dia (root)P = 0.0714360°⟂ axis30°crest flat = 0.0027–0.0064crest truncation 0.0024–0.0056root flat = 0.0027–0.0064root truncation 0.0024–0.0056H0.061859h0.057100 max0.050720 mintaper 1:16 on dia (1:32 on radius) · β = 1° 47′ 24″, included 2β = 3° 34′ 47″ · bisector ⟂ axisexternal thread (male)

External 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

plane 0 · E00.96768plane 1 · E10.98887plane 2 · E21.00178pipe OD D 1.0500MALE · 3/4-14 NPTRtrue scale (lengths and diameters); axis below, not drawnL1 0.3390 (4.75 thd)full thread 0.5457 (7.64 thd)V 0.2479L6 0.214 (3.00 thd) · E6 0.98110L2 − L6 0.332

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 —

DimensionBasicMaxMinTolerance
Major diameter D1Crest of the external thread at the gage plane1.046021.035130.01089
Pitch diameter E1Gage plane E1: L1 from the small end (external) or at the large end of the fitting (internal); gaging tolerance converted to diameter0.988870.988870.984410.00446
Minor diameter K1Root of the external thread at the gage plane0.938150.927270.01088
Allowance esNone: taper threads are made up to interference (NPT/NPTR); NPSC uses sealant—
Crest truncation fcTable 1 (both threads)0.0055710.002357
Root truncation frTable 1 (both threads)0.0055710.002357
Crest flat FcEquivalent width of flat0.0064290.002714
Root flat FrEquivalent width of flat0.0064290.002714

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
1 in 16 (0.75 in./ft)
Half apex angle of the pitch cone β
1.789911 °
Taper tolerance on the diameter, max / min
0.1250 / -0.0625 in/ft
Lead tolerance in the effective length ±
0.003 in
60° angle tolerance ±
2.0 °
Lead angle at the basic PD λ
1° 19′
Gaging method
NPT L1 thread gages (para. 5.2)
Gaging tolerance
1 turn small, 0 turns large from the modified basic (Table C-1)
Gaging position
End of the external thread 3 threads inside the face of the L1 ring (Table 5 col. 7)
Sealing
Mechanical joint, not a seal (section 5)

Basic pitch diameters and lengths Table 3

Pitch dia at the small end of the external thread E0
0.96768 in
Hand-tight engagement L1
0.3390 · 4.75 in, threads
Pitch dia at the hand-tight plane E1
0.98887 in
Effective external thread L2
0.5457 · 7.64 in, threads
Pitch dia at L2 E2
1.00178 in
Wrench make-up length L3
0.2143 · 3 in, threads
Pitch dia at the wrench make-up plane E3
0.95429 in
Complete external threads L5
0.4029 in
Pitch dia at L5 E5
0.99286 in
Vanish thread V
0.2479 · 3.47 in, threads
Overall external thread length L4
0.7935 in
Basic minor dia at the small end K0
0.9106 in
Change of diameter per turn
0.00446 in
Hand-tight engagement range, ± 1 turn
0.1961 – 0.4819 in
Wrench make-up interference on the PD
0.01339 in
Hand-tight plus wrench make-up length L1+L3
0.5533 in

NPTR (railing): shortened thread and recess Tables 4, 5

Shortening of the thread L6
0.214 · 3 in, threads
Pitch dia at the end of the external thread E6
0.9811 in
Effective thread of the NPTR external L2−L6
0.332 in
Maximum total external thread L4−L6
0.510 informula gives 0.511
Maximum incomplete threads due to chamfer V
0.179 in
Minimum depth of the recess in the fitting q
0.18 in
Minimum diameter of the recess Q
1.07 in
Minimum length T
0.25 in
Gage notch below the face of the fitting S
0.286 in

L1 plug and ring gages Tables 8 and 9

Plug gage major dia at the E0 plane
1.01525 in
Plug gage major dia at the gaging notch (E1)
1.03644 in
Plug gage major dia at the large end (E2)
1.04936 in
Gage pitch dia at the E0 plane
0.96768 in
Gage pitch dia at the gaging notch (E1)
0.98887 in
Gage pitch dia at the large end (E2)
1.00178 in
Ring gage minor dia at the E0 plane
0.92011 in
Ring gage minor dia at the gaging notch (E1)
0.94129 in
Thickness of the L1 ring or gage elements
0.3390 in
Working gage crest truncation
0.007143 in
Maximum standoff between plug and ring gages
0.038 in

Working gage tolerances Table 7

On the pitch diameter ±
0.0003 in
Lead, plugs / rings
0.0002 / 0.0003 in
Half angle ±, plugs / rings
10 / 15 min
Taper, plugs / rings
0.0006 / 0.0009 in
Major dia of plugs
0.0010 in
Minor dia of rings
0.0010 in
Total cumulative tolerance on the PD, plugs / rings
0.00097 / 0.00142 in

Notes

  • NPTR uses the NPT basic dimensions (Table 2) and NPT L1 gages; Table 5 gives the shortening L6, the recess and the gage-notch distance S. Table 5 values were not recalculated in 2013 (Foreword (d)). Para. 5.2 example (1/2-14): the start end of the modified basic thread lies 3 threads inside the face of the ring gage; gaging tolerance 2 turns large to 3 turns large. Max variation: no turns large and one turn small from the modified basic. Chamfer: external threads with chamfer smaller than the minor dia are gaged from the last scratch of the chamfer cone (para. 3.2.4.1, Fig. 5); otherwise from the end of the pipe (para. 3.2.4.3).
  • L4 − L6 (col. 10) = (L2 − L6) + V: printed 0.51, formula 0.511 (1 in last place, rounding); L2 − L6 threads (col. 9): printed 4.64, formula 4.65 (1 in last place, rounding); L4 − L6 threads (col. 11): printed 7.15, formula 7.14 (1 in last place, rounding)

Mates

3/4-14 NPTR 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

→ 3/4-14 NPT→ 3/4-14 NPSM→ 3/4-14 NPSL→ 1/2-14 NPTR→ 1-11.5 NPTR→ 3/4-14 NPTR internal
All values for 3/4-14 NPTRevery column of the workbook row
All values of the workbook row 3/4-14 NPTR
Designation3/4-14 NPTR
Decimal designation0.750-14 NPTR
Threads per inch14
Thread formTaper
SeriesNPTR
Series nameRailing Joint Taper Pipe Threads
External / internalExternal
Class—
Nominal pipe size3/4
Pitch P (in.)0.07142857
O.D. of pipe D, basic major dia (in.)1.050
Size category (Table 3 group)1/2, 3/4 (14 TPI)
Source tableTable 5
Printed page15
Where the diameter limits applyGage plane E1: L1 from the small end (external) or at the large end of the fitting (internal); gaging tolerance converted to diameter
Major dia max (in.)1.04602
Major dia min (in.)1.03513
Major dia tolerance (in.)0.01089
Major dia statusCalculated at the gage plane: PD limits with Table 1 truncation limits (para. 2.4)
Basic pitch dia at gage plane E1 (in.)0.98887
Pitch dia max (in.)0.98887
Pitch dia min (in.)0.98441
PD tolerance (in.)0.00446
Minor dia max (in.)0.93815
Minor dia min (in.)0.92727
Minor dia tolerance (in.)0.01088
Minor dia statusCalculated at the gage plane: PD limits with Table 1 truncation limits (para. 2.4)
Allowance sourceNone: 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 tolerance ± in effective length (in.)0.003
60° angle tolerance ± (deg)2.0
Taper tolerance max (in./ft)0.1250
Taper tolerance min (in./ft)-0.0625
Lead / angle / taper sourceTable 3, p. 10 (Table 3 is for NPT; NPTR has the NPT form, para. 5.1.2)
Lead angle at basic PD (deg)1.317131
Lead angle (deg min)1° 19′
Tensile stress area As (sq in.)not given in the standard
Thread angle (deg)60
Flank angle (deg)30
Sharp V height H (in.)0.0618590
Thread height h max (in.)0.0571
Thread height h min (in.)0.05072
Crest truncation min (in.)0.002357
Crest truncation max (in.)0.005571
Root truncation min (in.)0.002357
Root truncation max (in.)0.005571
Crest flat min (in.)0.002714
Crest flat max (in.)0.006429
Root flat min (in.)0.002714
Root flat max (in.)0.006429
Sweep cut: start diameter (in.)1.03825
Sweep cut: tip diameter (in.)0.92396
Sweep cut: depth (in.)0.057145
Sweep cut: profile width at start diameter (in.)0.068715
Sweep cut: tip flat (in.)0.002714
Sweep cut: start diameter isMajor dia at the small end (E6 plane), basic position; the blank is a 1:16 cone
Taper half-angle β (deg)1.789911
Taper on diameter1 in 16 (0.75 in./ft)
E0 pitch dia at small end (in.)0.96768
L1 hand-tight engagement (in.)0.3390
L1 (threads)4.75
E1 pitch dia at hand-tight plane (in.)0.98887
L2 effective thread, external (in.)0.5457
L2 (threads)7.64
E2 pitch dia at L2 plane (in.)1.00178
L2 − L1 (in.)0.2067
L2 − L1 (threads)2.89
L3 wrench make-up, internal (in.)0.2143
L3 (threads)3
E3 pitch dia at wrench make-up plane (in.)0.95429
V vanish thread (in.)0.2479
V (threads)3.47
L4 overall external thread length, reference (in.)0.7935
L5 complete external threads (in.)0.4029
E5 pitch dia at L5 plane (in.)0.99286
Height of thread h, Table 2 col. 22 (in.)0.05714
Change in dia per turn 0.0625/n (in.)0.00446
K0 basic minor dia at small end (in.)0.9106
E0 by formula D − (0.05D + 1.1)P0.96768
E1 by formula E0 + 0.0625·L10.98887
L2 by formula (0.80D + 6.8)P0.5457
E2 by formula E0 + 0.0625·L21.00179
E3 by formula E0 − 0.0625·L30.95428
L5 by formula L2 − 2P0.4029
E5 by formula E0 + 0.0625·L50.99286
V by formula 3.47P0.2479
L4 by formula L2 + V0.7936
K0 by formula E0 − 0.8P0.9105
Gaging methodNPT L1 thread gages (para. 5.2)
Gaging tolerance (turns)1 turn small, 0 turns large from the modified basic (Table C-1)
Gaging limit large (turns)0
Gaging limit small (turns)1
Basic gaging positionEnd of the external thread 3 threads inside the face of the L1 ring (Table 5 col. 7)
Hand-tight engagement min, ±1 turn both parts (in.)0.1961
Hand-tight engagement max, ±1 turn both parts (in.)0.4819
Wrench make-up interference on PD, basic L3/16 (in.)0.01339
Hand-tight + wrench make-up length L1 + L3 (in.)0.5533
SealingMechanical joint, not a seal (section 5)
E6 pitch dia at end of external thread (in.)0.9811
L6 shortening of thread (in.)0.214
L6 (threads)3
L2 − L6 effective thread (in.)0.332
L2 − L6 (threads)4.64
L4 − L6 max total external thread (in.)0.510
L4 − L6 (threads)7.15
V max incomplete threads due to chamfer (in.)0.179
V (threads)2.5
q min depth of recess in fitting (in.)0.18
Q min dia of recess in fitting (in.)1.07
T min length (in.)0.25
S distance gage notch below face of fitting (in.)0.286
S (threads)4
E6 by formula E0 + L6/160.9811
Gage: plug major dia at E0 plane (in.)1.01525
Gage: plug major dia at E1 gaging notch (in.)1.03644
Gage: plug major dia at E2 large end (in.)1.04936
Gage: pitch dia at E0 plane (in.)0.96768
Gage: pitch dia at E1 gaging notch (in.)0.98887
Gage: pitch dia at E2 large end (in.)1.00178
Gage: ring minor dia at E0 plane (in.)0.92011
Gage: ring minor dia at E1 gaging notch (in.)0.94129
Gage: thickness of L1 ring or gage elements (in.)0.3390
Gage: working gage crest truncation (in.)0.007143
Gage: root must clear 0.0381P width (in.)0.002721
Gage: plug major at E0 by formula E0 + (H − 2·trunc)1.01525
Working gage tol. on PD ± (in.)0.0003
Working gage tol. lead, plugs (in.)0.0002
Working gage tol. lead, rings (in.)0.0003
Working gage tol. half angle, plugs ± (min)10
Working gage tol. half angle, rings ± (min)15
Working gage tol. taper, plugs + (in.)0.0006
Working gage tol. taper, rings − (in.)0.0009
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.)0.00097
Working gage total cumulative tol. on PD, rings (in.)0.00142
Max standoff between plug and ring gages (in.)0.038
Check against formulasL4 − L6 (col. 10) = (L2 − L6) + V: printed 0.51, formula 0.511 (1 in last place, rounding); L2 − L6 threads (col. 9): printed 4.64, formula 4.65 (1 in last place, rounding); L4 − L6 threads (col. 11): printed 7.15, formula 7.14 (1 in last place, rounding)
NotesNPTR uses the NPT basic dimensions (Table 2) and NPT L1 gages; Table 5 gives the shortening L6, the recess and the gage-notch distance S. Table 5 values were not recalculated in 2013 (Foreword (d)). Para. 5.2 example (1/2-14): the start end of the modified basic thread lies 3 threads inside the face of the ring gage; gaging tolerance 2 turns large to 3 turns large. Max variation: no turns large and one turn small from the modified basic. Chamfer: external threads with chamfer smaller than the minor dia are gaged from the last scratch of the chamfer cone (para. 3.2.4.1, Fig. 5); otherwise from the end of the pipe (para. 3.2.4.3).
Lookup key3/4-14 NPTR · External

Related tools

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.