18" × 5 TPI BUTT (pull type) External Thread Specifications
18-5 BUTT-2A · 18.0000-5 BUTT-2A
ASMESTD: ASME B1.9SOURCE: Table 3, Tables 1, 2, 5TYPE: External (bolt/screw)CLASS: 2AFLANKS 7° / 45°ROOT: roundTable 1 combination
Thread profile
18-5 BUTT-2A: solid = maximum material, dotted = minimum material, dashed = basic profile before the allowance. Flanks 7° (pressure) and 45° (clearance) from the radial line, 52° thread angle; drawn to scale.
Limits of size, class 2A
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter dCrest of the male thread, max = D − G | 18.0000 | 17.9912 | 17.9780 | 0.0132 |
| Pitch diameter EMax = D − h − G | 17.8800 | 17.8712 | 17.8580 | 0.0132 |
| Minor diameter KsRoot of the male thread; min is a reference value | 17.7600 | 17.7261 | 17.6964ref. | 0.0297ref. |
| Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7) | 0.0088 | |||
| Root radius rRound root, male (Fig. 1a) | 0.014282 | 0.007140 | ||
| Thread engagement heh − G/2 at max, less the PD tolerance at min | 0.115600 | 0.102400 |
Dimensions in inches. Values are those of the standard (ASME B1.9); 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.
Mating female thread, limits of size, class 2B
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter DnRoot of the female thread, min = D + 0.12542p; max for reference | 18.0000 | 18.0548ref. | 18.0251 | |
| Pitch diameter EMin = D − h | 17.8800 | 17.8932 | 17.8800 | 0.0132 |
| Minor diameter KnCrest of the female thread, min = D − 2h | 17.7600 | 17.7732 | 17.7600 | 0.0132 |
| Root radius rRound root, female (Fig. 1a) | 0.014282 | 0.007140 |
Dimensions in inches. Values are those of the standard (ASME B1.9); 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.
Lead, flank angle and length of engagement
- Lead + flank variation limit Σ
- 0.01320 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
- Lead variation alone ±δl
- 0.00741 inAllowable lead error if there is no flank error
- 45° flank angle variation alone ±δα
- 3.474 °Half-angle error of the clearance flank
- 7° flank angle variation alone ±δα
- 7.333 °Half-angle error of the pressure flank
Gaging Sections 10, 11 · Tables 6, 7, 8, 11
Male thread 18-5 BUTT-2A
- Gage pitch tolerance (W)
- 0.00030 in
- Gage 7° flank angle tolerance
- 5 min
- Gage 45° flank angle tolerance
- 4 min
- Gage major / minor tolerance
- 0.0013 in
- Gage pitch diameter tolerance
- 0.00060 in
- PD equivalent of pitch and flank tolerance
- 0.0010 in
- GO pitch diameter limit
- 17.8712 in
- NOT GO pitch diameter limit
- 17.8580 in
- NOT GO truncated crest diameter
- 17.7880 in
- Setting plug truncated major diameter
- 17.9512 in
- Best-size wire
- 0.10829 · C = 0.16369 in, C
- Maximum wire
- 0.12287 · C = 0.20975 in, C
Female thread 18-5 BUTT-2B
- Gage pitch tolerance (X)
- 0.00040 in
- Gage flank angle tolerance
- 5 min
- Gage major / minor tolerance
- 0.0013 in
- Gage pitch diameter tolerance
- 0.00120 in
- PD equivalent of pitch and flank tolerance
- 0.0012 in
- GO pitch diameter limit
- 17.8800 in
- NOT GO pitch diameter limit
- 17.8932 in
- NOT GO truncated crest diameter
- 17.9632 in
- Plain gage tolerance
- 0.00070 in
- Root relief width GO
- 0.033400 in
- Root relief width NOT GO
- 0.050000 in
Notes
- Class 2: no taper/roundness requirement (para. 6.6.1).
Mates
18-5 BUTT-2A screws into a thread of the same standard at the same size and pitch. The standard mating internal thread is class 2B. 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 18-5 BUTT-2Aevery column of the workbook row
| Designation | 18-5 BUTT-2A |
|---|---|
| Decimal designation | 18.0000-5 BUTT-2A |
| Threads per inch | 5 |
| Thread form | BUTT |
| Series (Table 1) | BUTT |
| Series name | Pull type, rounded root (default) |
| External / internal | External |
| Class | 2A |
| Nominal size (in.) | 18 |
| Pitch P (in.) | 0.20000000 |
| Basic major dia D (in.) | 18.0000 |
| Size category | Table 1 combination |
| Source table | Table 3, Tables 1, 2, 5 |
| Printed page | 4, 5, 6, 10 |
| Major dia max (in.) | 17.9912 |
| Major dia min (in.) | 17.9780 |
| Major dia tolerance (in.) | 0.0132 |
| Major dia status | Toleranced: D - G (max), minus the PD tolerance (min) (paras. 6.2, 7) |
| Allowance G (in.; internal: mating external value, reference) | 0.0088 |
| Tolerance range (Tables 3-5) | Over 16 thru 24 |
| Range over (in.) | 16.0 |
| Range thru (in.) | 24.0 |
| Range mean dia for formula (in.) | 20.000 |
| Length of engagement Le = 10P (in.) | 2.0000 |
| Basic pitch dia E = D - h (in.) | 17.8800 |
| Pitch dia max (in.) | 17.8712 |
| Pitch dia min (in.) | 17.8580 |
| PD tolerance (in.) | 0.0132 |
| Basic minor dia K = D - 2h (in.) | 17.7600 |
| Minor dia max (in.) | 17.7261 |
| Minor dia min (in.) | 17.6964 |
| Minor dia tolerance (in.) | 0.0297 |
| Minor dia status | Max = D - 1.32542P - G; min is reference only = min PD - 0.80803P (para. 6.3, Sec. 4) |
| Root radius max (in.) | 0.014282 |
| Root radius min (in.) | 0.007140 |
| Root truncation s max (in.) | 0.016520 |
| Root truncation s min (in.) | 0.008260 |
| Engagement height he max (in.) | 0.115600 |
| Engagement height he min (in.) | 0.102400 |
| Lead + flank PD-equivalent limit (in.) | 0.01320 |
| Lead variation alone ± (in.) | 0.00741 |
| 45° flank variation alone ± (deg) | 3.474 |
| 7° flank variation alone ± (deg) | 7.333 |
| Lead angle at basic PD (deg) | 0.2040 |
| Lead angle (deg min) | 0° 12′ |
| Tensile stress area As (sq in.) | not given in the standard |
| Thread angle (deg) | 52 |
| Pressure (load) flank angle (deg) | 7 |
| Clearance flank angle (deg) | 45 |
| Flank orientation | Pull type (external thread pulls): 45° clearance flank leads, 7° load flank follows (Sec. 9) |
| Sharp V height H (in.) | 0.178128 |
| Basic thread engagement height h (in.) | 0.120000 |
| Thread height hs = hn (in.) | 0.132542 |
| Crest truncation f (in.) | 0.029064 |
| Crest width F (in.) | 0.032632 |
| Sweep cut: start diameter (in.) | 17.991200 |
| Sweep cut: tip diameter (in.) | 17.726100 |
| Sweep cut: depth (in.) | 0.132542 |
| Sweep cut: profile width at start diameter (in.) | 0.167368 |
| Sweep cut: tip width (root flat S max or radius r max) (in.) | 0.014282 |
| Constant c = 0.80803P (in.) | 0.161606 |
| PD tolerance component 0.00854√P (in.) | 0.003819 |
| W gage: pitch tolerance (in.) | 0.00030 |
| W gage: 7° flank tolerance (min) | 5 |
| W gage: 45° flank tolerance (min) | 4 |
| W gage: major/minor tolerance (in.) | 0.0013 |
| W gage: PD tolerance (in.) | 0.00060 |
| W gage: PD equivalent of pitch/flank tol. (in.) | 0.0010 |
| Z plain gage tolerance (in.) | 0.00070 |
| GO gage PD limit (in.) | 17.8712 |
| NOT GO gage PD limit (in.) | 17.8580 |
| NOT GO crest/minor truncated dia (in.) | 17.7880 |
| Setting plug truncated major dia (in.) | 17.9512 |
| Root relief width GO (0.167P) (in.) | 0.033400 |
| Root relief width NOT GO (0.25P) (in.) | 0.050000 |
| Best-size wire (in.) | 0.10829 |
| Measurement constant C, best wire (in.) | 0.16369 |
| Maximum wire (in.) | 0.12287 |
| Measurement constant C, max wire (in.) | 0.20975 |
| Check against formulas | OK |
| Notes | Class 2: no taper/roundness requirement (para. 6.6.1). |
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ASME B1.9: Buttress Inch Screw Threads. Source: workbook data (2026-10-10). Confirm against your licensed copy of the standard before use.