2 1/2-8 PTF-SAE-SHORT PTF-SAE SHORT External Thread Specifications

2 1/2-8 PTF-SAE SHORT

ASMESTD: ASME B1.20.3SOURCE: Table 4 · p. 8TYPE: External (bolt/screw)CLASS: —SERIES: PTF-SAE SHORTTAPER 1:16
Major diameter
2.8717 – 2.8566
max – min, at the gage plane
Pitch diameter
2.77388 – 2.76216
max – min, at the gage plane
Minor diameter
2.6846 – 2.6677
max – min, at the gage plane
Pitch
0.12500
8 threads per inch

Thread profile

gage plane: hand-tight, L1 from small endthread axisD1 = 2.8717–2.8566major dia (crest)E1 = 2.77388–2.76216pitch dia, basic 2.76216K1 = 2.6846–2.6677minor dia (root)P = 0.1250060°⟂ axis30°crest flat = 0.0060–0.0080crest truncation 0.0052–0.0069root flat = 0.0080–0.0110root truncation 0.0069–0.0095H0.108253h0.096153 max0.091853 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 · E02.72734D0 2.8235 · K0 2.6355plane 1 · E12.76216D1 2.8583 · K1 2.6703plane 2 · E22.79062D2 2.8868 · K2 2.6988pipe OD D 2.8750fitting OD D2 2.893MALE · 2 1/2-8 PTF-SAE SHORTtrue scale (lengths and diameters); axis below, not drawnL1 0.5570 (4.46 thd)full thread 1.0125 (8.10 thd)V 0.1250shoulder 1.3250

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 thread2.87172.85660.0151
Pitch diameter E1Hand-tight plane, L1 short from the small end (E1, Table 3)2.762162.773882.762160.01172
Minor diameter K1Root of the external thread2.68462.66770.0169
Crest truncation fcFig. 2, both threads0.00690.0052
Root truncation frFig. 2; at least the mating crest’s maximum0.00950.0069
Crest flat FcEquivalent width of flat (Fig. 2)0.0080.006
Root flat FrEquivalent width of flat (Fig. 2)0.0110.008

Dimensions in inches. Values are those of the standard (ASME B1.20.3); 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.

Diameters along the taper D major, E pitch, K minor (Table A1 notation), inches

PlaneE basicE maxE minD basicD maxD minK basicK maxK min
Plane 02.727342.739062.727342.82352.83692.82182.63552.64982.6329
Plane 12.762162.773882.762162.85832.87172.85662.67032.68462.6677
Plane 22.790622.802342.790622.88682.90022.88512.69882.71312.6962

The standard defines no basic major or minor diameter: D basic and K basic are calculated with the mean Fig. 2 truncations. On the taper every diameter changes by 0.0625 in. per inch of length.

Taper, lengths and gaging

Taper, gage and sealing para. 1.6, Fig. 1, Fig. 2

Taper on the diameter T
0.0625 ± 0.0050 in/in
Half apex angle of the pitch cone β
1° 47′ 24″
Included taper angle 2β
3° 34′ 47″
Taper on the radius
0.03125 in/in
Taper per thread on the diameter
0.007813 in
Gage tolerance, plus / minus ±
0 / 1.5 turns
Gage reference plane
Hand-tight plane, L1 short from the small end (E1, Table 3)
PD tolerance basis
Plus 0, minus 1-1/2 turns of the L1 gage (para. 1.6); L2/L3 gage within ±1/2 turn of the actual L1 position
Lead angle at the basic PD λ
0° 50′
Crest/root interference at flank contact, min – max δ
0.0000 – 0.0043 in
Recommended mating thread
NPSI (primary) or NPTF internal. Not designed for PTF-SAE SHORT internal or NPSF; at extreme tolerance limits may not assemble with them (Table 1 note 3)

Basic pitch diameters and lengths

Short-thread pitch dia at the small end E0s
2.72734 informula gives 2.72741
Pitch dia at the hand-tight plane E1
2.76216 in
Pitch dia at L2 E2
2.79062 in
Hand engagement L1
0.5570 · 4.46 in, turns
Wrench make-up L3
0.3750 · 0.02344 in, PD interference
Full external thread L2
1.0125 · 8.1 in, threads
Vanish threads V
0.3125 · 2.5 in, threads
Minimum shoulder length Ls
1.325 in
External thread for draw
0.4555 · 3.64 in, threads
OD of fitting D2
2.893 in
Engagement in a PTF-SAE SHORT internal thread Le
0.74 in

Notes

  • Conforms in all respects to NPTF except that one thread is removed (para. 1.4.1.2): at the small end of the external thread, at the large end of the internal thread. Gage tolerance read as turns of gage engagement: "minus" means fewer turns, i.e. a larger external thread and a smaller internal thread. This reading matches Table 1 notes 3 and 4. Limits at the gage plane are calculated: pitch diameter from the basic PD and the gage tolerance in turns x 0.0625p; major and minor diameters from the pitch-diameter limits, H = 0.866025p and the Fig. 2 truncation limits.
  • DIFFERS: E0 short printed 2.72734; formula D - (0.05D + 1.037)p of App. A.2 gives 2.72741 (-0.00007). The printed value equals E0 + 0.0625p (one thread taper added to Table 3 E0), so the 1.037 constant of A.2 is a rounding of 1.1 - 0.0625 = 1.0375. || Rounding only (last digit): Fig. 2 trunc min crest: printed 0.0052, 0.042p = 0.00525 (half-way value printed rounded down).

Mates

2 1/2-8 PTF-SAE SHORT screws into a thread of the same standard at the same size and pitch. The standard mating internal thread is class —. 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

→ 2 1/2-8 NPTF→ 2 1/2-8 PTF-SPL-SHORT→ 2 1/2-8 PTF-SPL-EXTRA-SHORT→ 2-11.5 PTF-SAE-SHORT→ 3-8 PTF-SAE-SHORT→ 2 1/2-8 PTF-SAE-SHORT internal
All values for 2 1/2-8 PTF-SAE SHORTevery column of the workbook row
All values of the workbook row 2 1/2-8 PTF-SAE SHORT
Designation2 1/2-8 PTF-SAE SHORT
Alternate designation2.8750 OD-8 PTF-SAE SHORT
Threads per inch8
Thread formDryseal 60°, taper 1:16
Series (Table 1)PTF-SAE SHORT
Series nameDryseal SAE Short Taper Pipe Thread
External / internalExternal
Class—
Nominal size2 1/2
Pitch P (in.)0.12500000
Pipe OD D, basic size (in.)2.875
Size categoryStandard series (para. 1.2)
Source tableTable 4
Printed page8
Thread type (para. 1.2)Type 2
Gage (reference) plane for the limitsHand-tight plane, L1 short from the small end (E1, Table 3)
Basic pitch dia at gage plane (in.)2.76216
Gage tolerance plus (turns)0
Gage tolerance minus (turns)1.5
PD tolerance basisPlus 0, minus 1-1/2 turns of the L1 gage (para. 1.6); L2/L3 gage within ±1/2 turn of the actual L1 position
Major dia max, D at gage plane (in.)2.8717
Major dia min, D at gage plane (in.)2.8566
Major dia tolerance, D (in.)0.0151
Pitch dia max, E at gage plane (in.)2.77388
Pitch dia min, E at gage plane (in.)2.76216
PD tolerance, E (in.)0.01172
Minor dia max, K at gage plane (in.)2.6846
Minor dia min, K at gage plane (in.)2.6677
Minor dia tolerance, K (in.)0.0169
Allowancenone (para. 1.3.2)
Root radiusnot specified; crests and roots may be rounded within the Fig. 2 truncation limits (para. 1.6)
Lead variation ±not given in B1.20.3 (gaging, B1.20.5)
Half-angle variation ±not given in B1.20.3 (gaging, B1.20.5)
Lead angle at basic PD (deg)0.8253
Lead angle (deg min)0° 50′
Stress areanot given in the standard
Thread angle (deg)60
Flank angle (deg)30
Sharp V height H (in.)0.108253
H as printed, Fig. 2 (in.)0.10825
Thread height h max (in.)0.096153
Thread height h min (in.)0.091853
Crest truncation min (in.)0.0052
Crest truncation max (in.)0.0069
Root truncation min (in.)0.0069
Root truncation max (in.)0.0095
Crest flat min (in.)0.006
Crest flat max (in.)0.008
Root flat min (in.)0.008
Root flat max (in.)0.011
Sweep cut: start diameter at gage plane (in.)2.8717
Sweep cut: tip diameter at gage plane (in.)2.6846
Sweep cut: depth (in.)0.09355
Sweep cut: tip flat (in.)0.0110
Sweep cut: profile width at start diameter (in.)0.11902
Crest flat as modelled (in.)0.00598
Sweep cut: taper on diameter (in./in.)0.0625
Check against formulasDIFFERS: E0 short printed 2.72734; formula D - (0.05D + 1.037)p of App. A.2 gives 2.72741 (-0.00007). The printed value equals E0 + 0.0625p (one thread taper added to Table 3 E0), so the 1.037 constant of A.2 is a rounding of 1.1 - 0.0625 = 1.0375. || Rounding only (last digit): Fig. 2 trunc min crest: printed 0.0052, 0.042p = 0.00525 (half-way value printed rounded down).
NotesConforms in all respects to NPTF except that one thread is removed (para. 1.4.1.2): at the small end of the external thread, at the large end of the internal thread. Gage tolerance read as turns of gage engagement: "minus" means fewer turns, i.e. a larger external thread and a smaller internal thread. This reading matches Table 1 notes 3 and 4. Limits at the gage plane are calculated: pitch diameter from the basic PD and the gage tolerance in turns x 0.0625p; major and minor diameters from the pitch-diameter limits, H = 0.866025p and the Fig. 2 truncation limits.
Taper on diameter (in./in.)0.0625
Taper tolerance ± (in./in.)0.0050
Half apex angle of pitch cone β (deg)1.7899
β (deg min sec)1° 47′ 24″
Included taper angle 2β (deg)3.5798
2β (deg min sec)3° 34′ 47″
Taper on radius (in./in.), 1 in 320.03125
β min from taper tolerance (deg)1.6468
β max from taper tolerance (deg)1.9330
Taper per thread on dia, 0.0625p (in.)0.007813
E0 short (in.)2.72734
E1: PD at hand-tight plane (in.)2.76216
E2: PD at L2, Table 3 (in.)2.79062
PD at end of this full external thread (in.)2.79062
PD at small end of external, max (in.)2.73906
PD at small end of external, min (in.)2.72734
Plane 0: distance from small end (ext) or face (int) (in.)0.0000
E0 basic: pitch dia at plane 0 (in.)2.72734
E0 max (in.)2.73906
E0 min (in.)2.72734
D0 basic, calculated (in.)2.8235
D0 max: major dia at plane 0 (in.)2.8369
D0 min (in.)2.8218
K0 basic, calculated (in.)2.6355
K0 max: minor dia at plane 0 (in.)2.6498
K0 min (in.)2.6329
Plane 1: distance from small end (ext) or face (int) (in.)0.5570
E1 basic: pitch dia at plane 1 (in.)2.76216
E1 max (in.)2.77388
E1 min (in.)2.76216
D1 basic, calculated (in.)2.8583
D1 max: major dia at plane 1 (in.)2.8717
D1 min (in.)2.8566
K1 basic, calculated (in.)2.6703
K1 max: minor dia at plane 1 (in.)2.6846
K1 min (in.)2.6677
Plane 2: distance from small end (ext) or face (int) (in.)1.0125
E2 basic: pitch dia at plane 2 (in.)2.79062
E2 max (in.)2.80234
E2 min (in.)2.79062
D2 basic, calculated (in.)2.8868
D2 max: major dia at plane 2 (in.)2.9002
D2 min (in.)2.8851
K2 basic, calculated (in.)2.6988
K2 max: minor dia at plane 2 (in.)2.7131
K2 min (in.)2.6962
Distance x measured fromsmall end of the external thread
PD change along x (+1 grows, −1 shrinks, 0 straight)1
E at x = 0, basic (in.)2.72734
Hand engagement L1 (in.)0.682
L1 (threads)5.46
Hand engagement L1 short (in.)0.557
L1 short (threads)4.46
Hand-tight engagement of this thread (in.)0.5570
Hand-tight engagement (turns)4.46
Wrench make-up L3 = 3p (in.)0.3750
PD interference from L3 make-up, on dia (in.)0.02344
Length of full external thread L2 (in.)1.0125
Full external thread (threads)8.1
Vanish thds V + 1p + 1/2p (in.)0.3125
V + 1p + 1/2p (threads)2.5
Minimum shoulder length L2 short + 2-1/2p (in.)1.325
External thread for draw (in.)0.4555
Draw (threads)3.64
OD of fitting D2 (in.)2.893
L2 / L3 gage correlation with L1 ± (turns)0.5
Crest/root interference at flank contact, min (radial, in.)0.0000
Crest/root interference at flank contact, max (radial, in.)0.0043
Table 2: engagement in NPSI internal (in.)0.93
Table 2: engagement in NPTF internal (in.)0.87
Table 2: engagement in NPSF internal (in.)0.81
Table 2: engagement in PTF-SAE SHORT internal (in.)0.74
Recommended mating thread (Table 1, C.3)NPSI (primary) or NPTF internal. Not designed for PTF-SAE SHORT internal or NPSF; at extreme tolerance limits may not assemble with them (Table 1 note 3)
Lookup key2 1/2-8 PTF-SAE SHORT | External

Related tools

ASME B1.20.3: Dryseal Pipe Threads, Inch. Source: workbook data (2026-10-10). Confirm against your licensed copy of the standard before use.