0.75" × 20 TPI BUTT (pull type) External Thread Specifications

0.75-20 BUTT-2A · 0.7500-20 BUTT-2A

ASMESTD: ASME B1.9SOURCE: Tables 1, 2 (tolerance calculated, Sec. 6.1)TYPE: External (bolt/screw)CLASS: 2AFLANKS 7° / 45°ROOT: roundTable 1 combination (footnote a)calculated, not printed in the standard

Thread profile

0.75-20 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

calculated, not printed in the standard.

Dimension	Basic	Max	Min	Tolerance
Major diameter dCrest of the male thread, max = D − G	0.7500	0.7462	0.7404	0.0058
Pitch diameter EMax = D − h − G	0.7200	0.7162	0.7104	0.0058
Minor diameter KsRoot of the male thread; min is a reference value	0.6900	0.6799	0.6700ref.	0.0099ref.
Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7)		0.0038
Root radius rRound root, male (Fig. 1a)		0.003571	0.001785
Thread engagement heh − G/2 at max, less the PD tolerance at min		0.028100	0.022300

Dimensions in inches. Values are those of the standard (ASME B1.9); this row is calculated. 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

calculated, not printed in the standard.

Dimension	Basic	Max	Min	Tolerance
Major diameter DnRoot of the female thread, min = D + 0.12542p; max for reference	0.7500	0.7662ref.	0.7563
Pitch diameter EMin = D − h	0.7200	0.7258	0.7200	0.0058
Minor diameter KnCrest of the female thread, min = D − 2h	0.6900	0.6958	0.6900	0.0058
Root radius rRound root, female (Fig. 1a)		0.003571	0.001785

Dimensions in inches. Values are those of the standard (ASME B1.9); this row is calculated. 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: 0.00580 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
Lead variation alone ±δl: 0.00326 inAllowable lead error if there is no flank error
45° flank angle variation alone ±δα: 6.105 °Half-angle error of the clearance flank
7° flank angle variation alone ±δα: 12.889 °Half-angle error of the pressure flank

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

Male thread 0.75-20 BUTT-2A

Gage pitch tolerance (W): 0.00015 in
Gage 7° flank angle tolerance: 15 min
Gage 45° flank angle tolerance: 8 min
Gage major / minor tolerance: 0.0005 in
Gage pitch diameter tolerance: 0.00015 in
PD equivalent of pitch and flank tolerance: 0.0005 in
GO pitch diameter limit: 0.7162 in
NOT GO pitch diameter limit: 0.7104 in
NOT GO truncated crest diameter: 0.6929 in
Setting plug truncated major diameter: 0.7362 in
Best-size wire: 0.02707 · C = 0.04093 in, C
Maximum wire: 0.03072 · C = 0.05245 in, C

Female thread 0.75-20 BUTT-2B

Gage pitch tolerance (X): 0.00030 in
Gage flank angle tolerance: 15 min
Gage major / minor tolerance: 0.0005 in
Gage pitch diameter tolerance: 0.00030 in
PD equivalent of pitch and flank tolerance: 0.0009 in
GO pitch diameter limit: 0.7200 in
NOT GO pitch diameter limit: 0.7258 in
NOT GO truncated crest diameter: 0.7433 in
Plain gage tolerance: 0.00010 in
Root relief width GO: 0.008350 in
Root relief width NOT GO: 0.012500 in

Notes

Table 1 lists 0.75-20 but Tables 3, 4 and 5 give no 20 TPI value above 0.7 in.; tolerance and allowance are calculated (range over 0.7 thru 1.0, mean 0.85 in.), not printed. Table 1 footnote a: best-size wire measurement of PD may be incorrect (double contact on the 7° flank, lead angle over 2°); see Table 11 maximum wire. Class 2: no taper/roundness requirement (para. 6.6.1).
Not tabulated: 20 TPI is not listed for over 0.7 thru 1.0 in Tables 3-5; PD tolerance and allowance calculated with the Sec. 6.1 / 7 formulas

Mates

0.75-20 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

→ 0.75" × 12 TPI → 0.75" × 16 TPI → 0.625" × 20 TPI → 0.875" × 10 TPI → 0.75" × 20 TPI internal

All values for 0.75-20 BUTT-2Aevery column of the workbook row

All values of the workbook row 0.75-20 BUTT-2A
Designation	0.75-20 BUTT-2A
Decimal designation	0.7500-20 BUTT-2A
Threads per inch	20
Thread form	BUTT
Series (Table 1)	BUTT
Series name	Pull type, rounded root (default)
External / internal	External
Class	2A
Nominal size (in.)	0.75
Pitch P (in.)	0.05000000
Basic major dia D (in.)	0.7500
Size category	Table 1 combination (footnote a)
Source table	Tables 1, 2 (tolerance calculated, Sec. 6.1)
Printed page	4, 5
Major dia max (in.)	0.7462
Major dia min (in.)	0.7404
Major dia tolerance (in.)	0.0058
Major dia status	Toleranced: D - G (max), minus the PD tolerance (min) (paras. 6.2, 7)
Allowance G (in.; internal: mating external value, reference)	0.0038
Tolerance range (Tables 3-5)	Over 0.7 thru 1.0
Range over (in.)	0.7
Range thru (in.)	1.0
Range mean dia for formula (in.)	0.850
Length of engagement Le = 10P (in.)	0.5000
Basic pitch dia E = D - h (in.)	0.7200
Pitch dia max (in.)	0.7162
Pitch dia min (in.)	0.7104
PD tolerance (in.)	0.0058
Basic minor dia K = D - 2h (in.)	0.6900
Minor dia max (in.)	0.6799
Minor dia min (in.)	0.6700
Minor dia tolerance (in.)	0.0099
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.)	0.003571
Root radius min (in.)	0.001785
Root truncation s max (in.)	0.004130
Root truncation s min (in.)	0.002065
Engagement height he max (in.)	0.028100
Engagement height he min (in.)	0.022300
Lead + flank PD-equivalent limit (in.)	0.00580
Lead variation alone ± (in.)	0.00326
45° flank variation alone ± (deg)	6.105
7° flank variation alone ± (deg)	12.889
Lead angle at basic PD (deg)	1.2663
Lead angle (deg min)	1° 16′
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.)	0.044532
Basic thread engagement height h (in.)	0.030000
Thread height hs = hn (in.)	0.033136
Crest truncation f (in.)	0.007266
Crest width F (in.)	0.008158
Sweep cut: start diameter (in.)	0.746200
Sweep cut: tip diameter (in.)	0.679900
Sweep cut: depth (in.)	0.033136
Sweep cut: profile width at start diameter (in.)	0.041842
Sweep cut: tip width (root flat S max or radius r max) (in.)	0.003571
Constant c = 0.80803P (in.)	0.040402
PD tolerance component 0.00854√P (in.)	0.001910
W gage: pitch tolerance (in.)	0.00015
W gage: 7° flank tolerance (min)	15
W gage: 45° flank tolerance (min)	8
W gage: major/minor tolerance (in.)	0.0005
W gage: PD tolerance (in.)	0.00015
W gage: PD equivalent of pitch/flank tol. (in.)	0.0005
Z plain gage tolerance (in.)	0.00010
GO gage PD limit (in.)	0.7162
NOT GO gage PD limit (in.)	0.7104
NOT GO crest/minor truncated dia (in.)	0.6929
Setting plug truncated major dia (in.)	0.7362
Root relief width GO (0.167P) (in.)	0.008350
Root relief width NOT GO (0.25P) (in.)	0.012500
Best-size wire (in.)	0.02707
Measurement constant C, best wire (in.)	0.04093
Maximum wire (in.)	0.03072
Measurement constant C, max wire (in.)	0.05245
Check against formulas	Not tabulated: 20 TPI is not listed for over 0.7 thru 1.0 in Tables 3-5; PD tolerance and allowance calculated with the Sec. 6.1 / 7 formulas
Notes	Table 1 lists 0.75-20 but Tables 3, 4 and 5 give no 20 TPI value above 0.7 in.; tolerance and allowance are calculated (range over 0.7 thru 1.0, mean 0.85 in.), not printed. Table 1 footnote a: best-size wire measurement of PD may be incorrect (double contact on the 7° flank, lead angle over 2°); see Table 11 maximum wire. 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.