1/4-18 PTF-SAE-SHORT PTF-SAE SHORT External Thread Specifications
1/4-18 PTF-SAE SHORT
ASMESTD: ASME B1.20.3SOURCE: Table 4 · p. 8TYPE: External (bolt/screw)CLASS: —SERIES: PTF-SAE SHORTTAPER 1:16
Major diameter
0.5398 – 0.5311
max – min, at the gage plane
Pitch diameter
0.49684 – 0.49163
max – min, at the gage plane
Minor diameter
0.4609 – 0.4521
max – min, at the gage plane
Pitch
0.05556
18 threads per inch
Thread profile
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
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 D1Crest of the external thread | 0.5398 | 0.5311 | 0.0087 | |
| Pitch diameter E1Hand-tight plane, L1 short from the small end (E1, Table 3) | 0.49163 | 0.49684 | 0.49163 | 0.00521 |
| Minor diameter K1Root of the external thread | 0.4609 | 0.4521 | 0.0088 | |
| Crest truncation fcFig. 2, both threads | 0.0043 | 0.0026 | ||
| Root truncation frFig. 2; at least the mating crest’s maximum | 0.0061 | 0.0043 | ||
| Crest flat FcEquivalent width of flat (Fig. 2) | 0.005 | 0.003 | ||
| Root flat FrEquivalent width of flat (Fig. 2) | 0.007 | 0.005 |
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
| Plane | E basic | E max | E min | D basic | D max | D min | K basic | K max | K min |
|---|---|---|---|---|---|---|---|---|---|
| Plane 0 | 0.48086 | 0.48607 | 0.48086 | 0.5221 | 0.5290 | 0.5204 | 0.4431 | 0.4502 | 0.4413 |
| Plane 1 | 0.49163 | 0.49684 | 0.49163 | 0.5328 | 0.5398 | 0.5311 | 0.4539 | 0.4609 | 0.4521 |
| Plane 2 | 0.50250 | 0.50771 | 0.50250 | 0.5437 | 0.5506 | 0.5420 | 0.4648 | 0.4718 | 0.4630 |
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
- 0.003472 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
- 2° 04′
- Crest/root interference at flank contact, min – max δ
- 0.0000 – 0.0035 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
- 0.48086 informula gives 0.48089
- Pitch dia at the hand-tight plane E1
- 0.49163 in
- Pitch dia at L2 E2
- 0.5025 in
- Hand engagement L1
- 0.1722 · 3.10 in, turns
- Wrench make-up L3
- 0.1667 · 0.01042 in, PD interference
- Full external thread L2
- 0.3462 · 6.23 in, threads
- Vanish threads V
- 0.1389 · 2.5 in, threads
- Minimum shoulder length Ls
- 0.4851 in
- External thread for draw
- 0.174 · 3.13 in, threads
- OD of fitting D2
- 0.546 in
- Engagement in a PTF-SAE SHORT internal thread Le
- 0.26 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 0.48086; formula D - (0.05D + 1.037)p of App. A.2 gives 0.48089 (-0.00003). 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): Table 4 L1s+4p: printed 0.3945, formula gives 0.3944 (+0.0001; internal full thread = L1 short + 4p)
Mates
1/4-18 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
All values for 1/4-18 PTF-SAE SHORTevery column of the workbook row
| Designation | 1/4-18 PTF-SAE SHORT |
|---|---|
| Alternate designation | 0.5400 OD-18 PTF-SAE SHORT |
| Threads per inch | 18 |
| Thread form | Dryseal 60°, taper 1:16 |
| Series (Table 1) | PTF-SAE SHORT |
| Series name | Dryseal SAE Short Taper Pipe Thread |
| External / internal | External |
| Class | — |
| Nominal size | 1/4 |
| Pitch P (in.) | 0.05555556 |
| Pipe OD D, basic size (in.) | 0.54 |
| Size category | Standard series (para. 1.2) |
| Source table | Table 4 |
| Printed page | 8 |
| Thread type (para. 1.2) | Type 2 |
| Gage (reference) plane for the limits | Hand-tight plane, L1 short from the small end (E1, Table 3) |
| Basic pitch dia at gage plane (in.) | 0.49163 |
| Gage tolerance plus (turns) | 0 |
| Gage tolerance minus (turns) | 1.5 |
| 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 |
| Major dia max, D at gage plane (in.) | 0.5398 |
| Major dia min, D at gage plane (in.) | 0.5311 |
| Major dia tolerance, D (in.) | 0.0087 |
| Pitch dia max, E at gage plane (in.) | 0.49684 |
| Pitch dia min, E at gage plane (in.) | 0.49163 |
| PD tolerance, E (in.) | 0.00521 |
| Minor dia max, K at gage plane (in.) | 0.4609 |
| Minor dia min, K at gage plane (in.) | 0.4521 |
| Minor dia tolerance, K (in.) | 0.0088 |
| Allowance | none (para. 1.3.2) |
| Root radius | not 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) | 2.0600 |
| Lead angle (deg min) | 2° 04′ |
| Stress area | not given in the standard |
| Thread angle (deg) | 60 |
| Flank angle (deg) | 30 |
| Sharp V height H (in.) | 0.048113 |
| H as printed, Fig. 2 (in.) | 0.04811 |
| Thread height h max (in.) | 0.041213 |
| Thread height h min (in.) | 0.037713 |
| Crest truncation min (in.) | 0.0026 |
| Crest truncation max (in.) | 0.0043 |
| Root truncation min (in.) | 0.0043 |
| Root truncation max (in.) | 0.0061 |
| Crest flat min (in.) | 0.003 |
| Crest flat max (in.) | 0.005 |
| Root flat min (in.) | 0.005 |
| Root flat max (in.) | 0.007 |
| Sweep cut: start diameter at gage plane (in.) | 0.5398 |
| Sweep cut: tip diameter at gage plane (in.) | 0.4609 |
| Sweep cut: depth (in.) | 0.03945 |
| Sweep cut: tip flat (in.) | 0.0070 |
| Sweep cut: profile width at start diameter (in.) | 0.05255 |
| Crest flat as modelled (in.) | 0.00301 |
| Sweep cut: taper on diameter (in./in.) | 0.0625 |
| Check against formulas | DIFFERS: E0 short printed 0.48086; formula D - (0.05D + 1.037)p of App. A.2 gives 0.48089 (-0.00003). 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): Table 4 L1s+4p: printed 0.3945, formula gives 0.3944 (+0.0001; internal full thread = L1 short + 4p) |
| 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. |
| 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 32 | 0.03125 |
| β min from taper tolerance (deg) | 1.6468 |
| β max from taper tolerance (deg) | 1.9330 |
| Taper per thread on dia, 0.0625p (in.) | 0.003472 |
| E0 short (in.) | 0.48086 |
| E1: PD at hand-tight plane (in.) | 0.49163 |
| E2: PD at L2, Table 3 (in.) | 0.5025 |
| PD at end of this full external thread (in.) | 0.50250 |
| PD at small end of external, max (in.) | 0.48607 |
| PD at small end of external, min (in.) | 0.48086 |
| Plane 0: distance from small end (ext) or face (int) (in.) | 0.0000 |
| E0 basic: pitch dia at plane 0 (in.) | 0.48086 |
| E0 max (in.) | 0.48607 |
| E0 min (in.) | 0.48086 |
| D0 basic, calculated (in.) | 0.5221 |
| D0 max: major dia at plane 0 (in.) | 0.5290 |
| D0 min (in.) | 0.5204 |
| K0 basic, calculated (in.) | 0.4431 |
| K0 max: minor dia at plane 0 (in.) | 0.4502 |
| K0 min (in.) | 0.4413 |
| Plane 1: distance from small end (ext) or face (int) (in.) | 0.1722 |
| E1 basic: pitch dia at plane 1 (in.) | 0.49163 |
| E1 max (in.) | 0.49684 |
| E1 min (in.) | 0.49163 |
| D1 basic, calculated (in.) | 0.5328 |
| D1 max: major dia at plane 1 (in.) | 0.5398 |
| D1 min (in.) | 0.5311 |
| K1 basic, calculated (in.) | 0.4539 |
| K1 max: minor dia at plane 1 (in.) | 0.4609 |
| K1 min (in.) | 0.4521 |
| Plane 2: distance from small end (ext) or face (int) (in.) | 0.3462 |
| E2 basic: pitch dia at plane 2 (in.) | 0.50250 |
| E2 max (in.) | 0.50771 |
| E2 min (in.) | 0.50250 |
| D2 basic, calculated (in.) | 0.5437 |
| D2 max: major dia at plane 2 (in.) | 0.5506 |
| D2 min (in.) | 0.5420 |
| K2 basic, calculated (in.) | 0.4648 |
| K2 max: minor dia at plane 2 (in.) | 0.4718 |
| K2 min (in.) | 0.4630 |
| Distance x measured from | small end of the external thread |
| PD change along x (+1 grows, −1 shrinks, 0 straight) | 1 |
| E at x = 0, basic (in.) | 0.48086 |
| Hand engagement L1 (in.) | 0.2278 |
| L1 (threads) | 4.1 |
| Hand engagement L1 short (in.) | 0.1722 |
| L1 short (threads) | 3.1 |
| Hand-tight engagement of this thread (in.) | 0.1722 |
| Hand-tight engagement (turns) | 3.10 |
| Wrench make-up L3 = 3p (in.) | 0.1667 |
| PD interference from L3 make-up, on dia (in.) | 0.01042 |
| Length of full external thread L2 (in.) | 0.3462 |
| Full external thread (threads) | 6.23 |
| Vanish thds V + 1p + 1/2p (in.) | 0.1389 |
| V + 1p + 1/2p (threads) | 2.5 |
| Minimum shoulder length L2 short + 2-1/2p (in.) | 0.4851 |
| External thread for draw (in.) | 0.174 |
| Draw (threads) | 3.13 |
| OD of fitting D2 (in.) | 0.546 |
| 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.) | 0.0035 |
| Table 2: engagement in NPSI internal (in.) | 0.34 |
| Table 2: engagement in NPTF internal (in.) | 0.31 |
| Table 2: engagement in NPSF internal (in.) | 0.28 |
| Table 2: engagement in PTF-SAE SHORT internal (in.) | 0.26 |
| 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 key | 1/4-18 PTF-SAE SHORT | External |
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ASME B1.20.3: Dryseal Pipe Threads, Inch. Source: workbook data (2026-10-10). Confirm against your licensed copy of the standard before use.