1.25" × 8 TPI PUSH-BUTT (push type) External Thread Specifications

1.25-8 PUSH-BUTT-2A · 1.2500-8 PUSH-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

1.25-8 PUSH-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	1.2500	1.2445	1.2362	0.0083
Pitch diameter EMax = D − h − G	1.1750	1.1695	1.1612	0.0083
Minor diameter KsRoot of the male thread; min is a reference value	1.1000	1.0788	1.0602ref.	0.0186ref.
Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7)		0.0055
Root radius rRound root, male (Fig. 1a)		0.008926	0.004463
Thread engagement heh − G/2 at max, less the PD tolerance at min		0.072250	0.063950

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	1.2500	1.2843ref.	1.2657
Pitch diameter EMin = D − h	1.1750	1.1833	1.1750	0.0083
Minor diameter KnCrest of the female thread, min = D − 2h	1.1000	1.1083	1.1000	0.0083
Root radius rRound root, female (Fig. 1a)		0.008926	0.004463

Lead, flank angle and length of engagement

Lead + flank variation limit Σ: 0.00830 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
Lead variation alone ±δl: 0.00466 inAllowable lead error if there is no flank error
45° flank angle variation alone ±δα: 3.495 °Half-angle error of the clearance flank
7° flank angle variation alone ±δα: 7.378 °Half-angle error of the pressure flank

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

Male thread 1.25-8 PUSH-BUTT-2A

Gage pitch tolerance (W): 0.00025 in
Gage 7° flank angle tolerance: 5 min
Gage 45° flank angle tolerance: 5 min
Gage major / minor tolerance: 0.0007 in
Gage pitch diameter tolerance: 0.00020 in
PD equivalent of pitch and flank tolerance: 0.0007 in
GO pitch diameter limit: 1.1695 in
NOT GO pitch diameter limit: 1.1612 in
NOT GO truncated crest diameter: 1.1175 in
Setting plug truncated major diameter: 1.2195 in
Best-size wire: 0.06768 · C = 0.10233 in, C
Maximum wire: 0.07679 · C = 0.13109 in, C

Female thread 1.25-8 PUSH-BUTT-2B

Gage pitch tolerance (X): 0.00040 in
Gage flank angle tolerance: 5 min
Gage major / minor tolerance: 0.0007 in
Gage pitch diameter tolerance: 0.00040 in
PD equivalent of pitch and flank tolerance: 0.0010 in
GO pitch diameter limit: 1.1750 in
NOT GO pitch diameter limit: 1.1833 in
NOT GO truncated crest diameter: 1.2271 in
Plain gage tolerance: 0.00012 in
Root relief width GO: 0.020875 in
Root relief width NOT GO: 0.031250 in

Notes

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

Mates

1.25-8 PUSH-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

→ 1.25" × 10 TPI → 1.25" × 12 TPI → 1.25" × 16 TPI → 1.25" × 6 TPI → 1" × 16 TPI → 1.375" × 10 TPI → 1.25" × 8 TPI internal

All values for 1.25-8 PUSH-BUTT-2Aevery column of the workbook row

All values of the workbook row 1.25-8 PUSH-BUTT-2A
Designation	1.25-8 PUSH-BUTT-2A
Decimal designation	1.2500-8 PUSH-BUTT-2A
Threads per inch	8
Thread form	PUSH-BUTT
Series (Table 1)	PUSH-BUTT
Series name	Push type, rounded root
External / internal	External
Class	2A
Nominal size (in.)	1.25
Pitch P (in.)	0.12500000
Basic major dia D (in.)	1.2500
Size category	Table 1 combination
Source table	Table 3, Tables 1, 2, 5
Printed page	4, 5, 6, 10
Major dia max (in.)	1.2445
Major dia min (in.)	1.2362
Major dia tolerance (in.)	0.0083
Major dia status	Toleranced: D - G (max), minus the PD tolerance (min) (paras. 6.2, 7)
Allowance G (in.; internal: mating external value, reference)	0.0055
Tolerance range (Tables 3-5)	Over 1.0 thru 1.5
Range over (in.)	1.0
Range thru (in.)	1.5
Range mean dia for formula (in.)	1.250
Length of engagement Le = 10P (in.)	1.2500
Basic pitch dia E = D - h (in.)	1.1750
Pitch dia max (in.)	1.1695
Pitch dia min (in.)	1.1612
PD tolerance (in.)	0.0083
Basic minor dia K = D - 2h (in.)	1.1000
Minor dia max (in.)	1.0788
Minor dia min (in.)	1.0602
Minor dia tolerance (in.)	0.0186
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.)	0.008926
Root radius min (in.)	0.004463
Root truncation s max (in.)	0.010325
Root truncation s min (in.)	0.005163
Engagement height he max (in.)	0.072250
Engagement height he min (in.)	0.063950
Lead + flank PD-equivalent limit (in.)	0.00830
Lead variation alone ± (in.)	0.00466
45° flank variation alone ± (deg)	3.495
7° flank variation alone ± (deg)	7.378
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	Push type (external thread pushes): 7° load flank leads, 45° clearance flank follows (Sec. 9)
Sharp V height H (in.)	0.111330
Basic thread engagement height h (in.)	0.075000
Thread height hs = hn (in.)	0.082839
Crest truncation f (in.)	0.018165
Crest width F (in.)	0.020395
Sweep cut: start diameter (in.)	1.244500
Sweep cut: tip diameter (in.)	1.078800
Sweep cut: depth (in.)	0.082839
Sweep cut: profile width at start diameter (in.)	0.104605
Sweep cut: tip width (root flat S max or radius r max) (in.)	0.008926
Constant c = 0.80803P (in.)	0.101004
PD tolerance component 0.00854√P (in.)	0.003019
W gage: pitch tolerance (in.)	0.00025
W gage: 7° flank tolerance (min)	5
W gage: 45° flank tolerance (min)	5
W gage: major/minor tolerance (in.)	0.0007
W gage: PD tolerance (in.)	0.00020
W gage: PD equivalent of pitch/flank tol. (in.)	0.0007
Z plain gage tolerance (in.)	0.00012
GO gage PD limit (in.)	1.1695
NOT GO gage PD limit (in.)	1.1612
NOT GO crest/minor truncated dia (in.)	1.1175
Setting plug truncated major dia (in.)	1.2195
Root relief width GO (0.167P) (in.)	0.020875
Root relief width NOT GO (0.25P) (in.)	0.031250
Best-size wire (in.)	0.06768
Measurement constant C, best wire (in.)	0.10233
Maximum wire (in.)	0.07679
Measurement constant C, max wire (in.)	0.13109
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.