2.5" × 4 TPI BUTT (pull type) Internal Thread Specifications

2.5-4 BUTT-2B · 2.5000-4 BUTT-2B

ASMESTD: ASME B1.9SOURCE: Table 3, Tables 1, 2, 5TYPE: Internal (nut/tapped hole)CLASS: 2BFLANKS 7° / 45°ROOT: roundTable 1 combination

Thread profile

2.5-4 BUTT-2B: solid = maximum material, dotted = minimum material. Flanks 7° (pressure) and 45° (clearance) from the radial line, 52° thread angle; drawn to scale.

Limits of size, class 2B

Dimension	Basic	Max	Min	Tolerance
Major diameter DnRoot of the female thread, min = D + 0.12542p; max for reference	2.5000	2.5632ref.	2.5314
Pitch diameter EMin = D − h	2.3500	2.3612	2.3500	0.0112
Minor diameter KnCrest of the female thread, min = D − 2h	2.2000	2.2112	2.2000	0.0112
Root radius rRound root, female (Fig. 1a)		0.017853	0.008925

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 male thread, limits of size, class 2A

Dimension	Basic	Max	Min	Tolerance
Major diameter dCrest of the male thread, max = D − G	2.5000	2.4926	2.4814	0.0112
Pitch diameter EMax = D − h − G	2.3500	2.3426	2.3314	0.0112
Minor diameter KsRoot of the male thread; min is a reference value	2.2000	2.1612	2.1294ref.	0.0318ref.
Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7)		0.0074
Root radius rRound root, male (Fig. 1a)		0.017853	0.008925
Thread engagement heh − G/2 at max, less the PD tolerance at min		0.146300	0.135100

Lead, flank angle and length of engagement

Lead + flank variation limit Σ: 0.01120 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
Lead variation alone ±δl: 0.00629 inAllowable lead error if there is no flank error
45° flank angle variation alone ±δα: 2.358 °Half-angle error of the clearance flank
7° flank angle variation alone ±δα: 4.978 °Half-angle error of the pressure flank

Gaging Sections 10, 11 · Tables 6, 7, 8, 11

Male thread 2.5-4 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: 0.0009 in
Gage pitch diameter tolerance: 0.00025 in
PD equivalent of pitch and flank tolerance: 0.0010 in
GO pitch diameter limit: 2.3426 in
NOT GO pitch diameter limit: 2.3314 in
NOT GO truncated crest diameter: 2.2439 in
Setting plug truncated major diameter: 2.4426 in
Best-size wire: 0.13537 · C = 0.20469 in, C
Maximum wire: 0.15358 · C = 0.26217 in, C

Female thread 2.5-4 BUTT-2B

Gage pitch tolerance (X): 0.00040 in
Gage flank angle tolerance: 5 min
Gage major / minor tolerance: 0.0009 in
Gage pitch diameter tolerance: 0.00050 in
PD equivalent of pitch and flank tolerance: 0.0013 in
GO pitch diameter limit: 2.3500 in
NOT GO pitch diameter limit: 2.3612 in
NOT GO truncated crest diameter: 2.4487 in
Plain gage tolerance: 0.00016 in
Root relief width GO: 0.041750 in
Root relief width NOT GO: 0.062500 in

Notes

Class 2: no taper/roundness requirement (para. 6.6.1).

Mates

2.5-4 BUTT-2B takes a thread of the same standard at the same size and pitch. The standard mating external thread is class 2A. 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

→ 2.5" × 10 TPI → 2.5" × 12 TPI → 2.5" × 16 TPI → 2.5" × 5 TPI → 2.5" × 6 TPI → 2.5" × 8 TPI → 2.25" × 8 TPI → 2.75" × 10 TPI → 2.5" × 4 TPI external

All values for 2.5-4 BUTT-2Bevery column of the workbook row

All values of the workbook row 2.5-4 BUTT-2B
Designation	2.5-4 BUTT-2B
Decimal designation	2.5000-4 BUTT-2B
Threads per inch	4
Thread form	BUTT
Series (Table 1)	BUTT
Series name	Pull type, rounded root (default)
External / internal	Internal
Class	2B
Nominal size (in.)	2.5
Pitch P (in.)	0.25000000
Basic major dia D (in.)	2.5000
Size category	Table 1 combination
Source table	Table 3, Tables 1, 2, 5
Printed page	4, 5, 6, 10
Major dia max (in.)	2.5632
Major dia min (in.)	2.5314
Major dia status	Min = D + 0.12542P (basic); max is reference only = max PD + 0.80803P (para. 6.3, Sec. 4); no tolerance specified
Allowance G (in.; internal: mating external value, reference)	0.0074
Tolerance range (Tables 3-5)	Over 1.5 thru 2.5
Range over (in.)	1.5
Range thru (in.)	2.5
Range mean dia for formula (in.)	2.000
Length of engagement Le = 10P (in.)	2.5000
Basic pitch dia E = D - h (in.)	2.3500
Pitch dia max (in.)	2.3612
Pitch dia min (in.)	2.3500
PD tolerance (in.)	0.0112
Basic minor dia K = D - 2h (in.)	2.2000
Minor dia max (in.)	2.2112
Minor dia min (in.)	2.2000
Minor dia tolerance (in.)	0.0112
Minor dia status	Toleranced: min = D - 2h (basic), max = min + PD tolerance (para. 6.2)
Root radius max (in.)	0.017853
Root radius min (in.)	0.008925
Root truncation s max (in.)	0.020650
Root truncation s min (in.)	0.010325
Engagement height he max (in.)	0.146300
Engagement height he min (in.)	0.135100
Lead + flank PD-equivalent limit (in.)	0.01120
Lead variation alone ± (in.)	0.00629
45° flank variation alone ± (deg)	2.358
7° flank variation alone ± (deg)	4.978
Lead angle at basic PD (deg)	1.9395
Lead angle (deg min)	1° 56′
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.)	0.222660
Basic thread engagement height h (in.)	0.150000
Thread height hs = hn (in.)	0.165678
Crest truncation f (in.)	0.036330
Crest width F (in.)	0.040790
Sweep cut: start diameter (in.)	2.200000
Sweep cut: tip diameter (in.)	2.531400
Sweep cut: depth (in.)	0.165678
Sweep cut: profile width at start diameter (in.)	0.209210
Sweep cut: tip width (root flat S max or radius r max) (in.)	0.017853
Constant c = 0.80803P (in.)	0.202008
PD tolerance component 0.00854√P (in.)	0.004270
X gage: pitch tolerance (in.)	0.00040
X gage: flank angle tolerance (min)	5
X gage: major/minor tolerance (in.)	0.0009
X gage: PD tolerance (in.)	0.00050
X gage: PD equivalent of pitch/flank tol. (in.)	0.0013
Z plain gage tolerance (in.)	0.00016
GO gage PD limit (in.)	2.3500
NOT GO gage PD limit (in.)	2.3612
NOT GO crest/minor truncated dia (in.)	2.4487
Root relief width GO (0.167P) (in.)	0.041750
Root relief width NOT GO (0.25P) (in.)	0.062500
Check against formulas	OK
Notes	Class 2: no taper/roundness requirement (para. 6.6.1).

ASME B1.9: Buttress Inch Screw Threads. Source: workbook data (2026-10-10). Confirm against your licensed copy of the standard before use.