3" × 8 TPI BUTT (pull type) Internal Thread Specifications

3-8 BUTT-2B · 3.0000-8 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

3-8 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	3.0000	3.0351ref.	3.0157
Pitch diameter EMin = D − h	2.9250	2.9341	2.9250	0.0091
Minor diameter KnCrest of the female thread, min = D − 2h	2.8500	2.8591	2.8500	0.0091
Root radius rRound root, female (Fig. 1a)		0.008926	0.004463

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	3.0000	2.9939	2.9848	0.0091
Pitch diameter EMax = D − h − G	2.9250	2.9189	2.9098	0.0091
Minor diameter KsRoot of the male thread; min is a reference value	2.8500	2.8282	2.8088ref.	0.0194ref.
Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7)		0.0061
Root radius rRound root, male (Fig. 1a)		0.008926	0.004463
Thread engagement heh − G/2 at max, less the PD tolerance at min		0.071950	0.062850

Lead, flank angle and length of engagement

Lead + flank variation limit Σ: 0.00910 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
Lead variation alone ±δl: 0.00511 inAllowable lead error if there is no flank error
45° flank angle variation alone ±δα: 3.832 °Half-angle error of the clearance flank
7° flank angle variation alone ±δα: 8.089 °Half-angle error of the pressure flank

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

Male thread 3-8 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: 0.00025 in
PD equivalent of pitch and flank tolerance: 0.0007 in
GO pitch diameter limit: 2.9189 in
NOT GO pitch diameter limit: 2.9098 in
NOT GO truncated crest diameter: 2.8661 in
Setting plug truncated major diameter: 2.9689 in
Best-size wire: 0.06768 · C = 0.10233 in, C
Maximum wire: 0.07679 · C = 0.13109 in, C

Female thread 3-8 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: 0.00050 in
PD equivalent of pitch and flank tolerance: 0.0010 in
GO pitch diameter limit: 2.9250 in
NOT GO pitch diameter limit: 2.9341 in
NOT GO truncated crest diameter: 2.9779 in
Plain gage tolerance: 0.00020 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

3-8 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

→ 3" × 10 TPI → 3" × 12 TPI → 3" × 16 TPI → 3" × 4 TPI → 3" × 5 TPI → 3" × 6 TPI → 2.75" × 8 TPI → 3.5" × 10 TPI → 3" × 8 TPI external

All values for 3-8 BUTT-2Bevery column of the workbook row

All values of the workbook row 3-8 BUTT-2B
Designation	3-8 BUTT-2B
Decimal designation	3.0000-8 BUTT-2B
Threads per inch	8
Thread form	BUTT
Series (Table 1)	BUTT
Series name	Pull type, rounded root (default)
External / internal	Internal
Class	2B
Nominal size (in.)	3
Pitch P (in.)	0.12500000
Basic major dia D (in.)	3.0000
Size category	Table 1 combination
Source table	Table 3, Tables 1, 2, 5
Printed page	4, 5, 6, 10
Major dia max (in.)	3.0351
Major dia min (in.)	3.0157
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)	0.0061
Tolerance range (Tables 3-5)	Over 2.5 thru 4
Range over (in.)	2.5
Range thru (in.)	4.0
Range mean dia for formula (in.)	3.250
Length of engagement Le = 10P (in.)	1.2500
Basic pitch dia E = D - h (in.)	2.9250
Pitch dia max (in.)	2.9341
Pitch dia min (in.)	2.9250
PD tolerance (in.)	0.0091
Basic minor dia K = D - 2h (in.)	2.8500
Minor dia max (in.)	2.8591
Minor dia min (in.)	2.8500
Minor dia tolerance (in.)	0.0091
Minor dia status	Toleranced: min = D - 2h (basic), max = min + PD tolerance (para. 6.2)
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.)	0.071950
Engagement height he min (in.)	0.062850
Lead + flank PD-equivalent limit (in.)	0.00910
Lead variation alone ± (in.)	0.00511
45° flank variation alone ± (deg)	3.832
7° flank variation alone ± (deg)	8.089
Lead angle at basic PD (deg)	0.7793
Lead angle (deg min)	0° 47′
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.)	0.111330
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.)	2.850000
Sweep cut: tip diameter (in.)	3.015700
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
X gage: pitch tolerance (in.)	0.00040
X gage: flank angle tolerance (min)	5
X gage: major/minor tolerance (in.)	0.0007
X gage: PD tolerance (in.)	0.00050
X gage: PD equivalent of pitch/flank tol. (in.)	0.0010
Z plain gage tolerance (in.)	0.00020
GO gage PD limit (in.)	2.9250
NOT GO gage PD limit (in.)	2.9341
NOT GO crest/minor truncated dia (in.)	2.9779
Root relief width GO (0.167P) (in.)	0.020875
Root relief width NOT GO (0.25P) (in.)	0.031250
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.