0.5" × 20 TPI BUTT (pull type) Internal Thread Specifications

0.5-20 BUTT-2B · 0.5000-20 BUTT-2B

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

Thread profile

0.5-20 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	0.5000	0.5160ref.	0.5063
Pitch diameter EMin = D − h	0.4700	0.4756	0.4700	0.0056
Minor diameter KnCrest of the female thread, min = D − 2h	0.4400	0.4456	0.4400	0.0056
Root radius rRound root, female (Fig. 1a)		0.003571	0.001785

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	0.5000	0.4963	0.4907	0.0056
Pitch diameter EMax = D − h − G	0.4700	0.4663	0.4607	0.0056
Minor diameter KsRoot of the male thread; min is a reference value	0.4400	0.4300	0.4203ref.	0.0097ref.
Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7)		0.0037
Root radius rRound root, male (Fig. 1a)		0.003571	0.001785
Thread engagement heh − G/2 at max, less the PD tolerance at min		0.028150	0.022550

Lead, flank angle and length of engagement

Lead + flank variation limit Σ: 0.00560 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
Lead variation alone ±δl: 0.00314 inAllowable lead error if there is no flank error
45° flank angle variation alone ±δα: 5.895 °Half-angle error of the clearance flank
7° flank angle variation alone ±δα: 12.444 °Half-angle error of the pressure flank

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

Male thread 0.5-20 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: 0.4663 in
NOT GO pitch diameter limit: 0.4607 in
NOT GO truncated crest diameter: 0.4432 in
Setting plug truncated major diameter: 0.4863 in
Best-size wire: 0.02707 · C = 0.04093 in, C
Maximum wire: 0.03072 · C = 0.05245 in, C

Female thread 0.5-20 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: 0.4700 in
NOT GO pitch diameter limit: 0.4756 in
NOT GO truncated crest diameter: 0.4931 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 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).

Mates

0.5-20 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

→ 0.5" × 12 TPI → 0.5" × 16 TPI → 0.625" × 12 TPI → 0.5" × 20 TPI external

All values for 0.5-20 BUTT-2Bevery column of the workbook row

All values of the workbook row 0.5-20 BUTT-2B
Designation	0.5-20 BUTT-2B
Decimal designation	0.5000-20 BUTT-2B
Threads per inch	20
Thread form	BUTT
Series (Table 1)	BUTT
Series name	Pull type, rounded root (default)
External / internal	Internal
Class	2B
Nominal size (in.)	0.5
Pitch P (in.)	0.05000000
Basic major dia D (in.)	0.5000
Size category	Table 1 combination (footnote a)
Source table	Table 3, Tables 1, 2, 5
Printed page	4, 5, 6, 10
Major dia max (in.)	0.5160
Major dia min (in.)	0.5063
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)	0.0037
Tolerance range (Tables 3-5)	From 0.5 thru 0.7
Range over (in.)	0.5
Range thru (in.)	0.7
Range mean dia for formula (in.)	0.600
Length of engagement Le = 10P (in.)	0.5000
Basic pitch dia E = D - h (in.)	0.4700
Pitch dia max (in.)	0.4756
Pitch dia min (in.)	0.4700
PD tolerance (in.)	0.0056
Basic minor dia K = D - 2h (in.)	0.4400
Minor dia max (in.)	0.4456
Minor dia min (in.)	0.4400
Minor dia tolerance (in.)	0.0056
Minor dia status	Toleranced: min = D - 2h (basic), max = min + PD tolerance (para. 6.2)
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.)	0.028150
Engagement height he min (in.)	0.022550
Lead + flank PD-equivalent limit (in.)	0.00560
Lead variation alone ± (in.)	0.00314
45° flank variation alone ± (deg)	5.895
7° flank variation alone ± (deg)	12.444
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.)	0.044532
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.)	0.440000
Sweep cut: tip diameter (in.)	0.506300
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
X gage: pitch tolerance (in.)	0.00030
X gage: flank angle tolerance (min)	15
X gage: major/minor tolerance (in.)	0.0005
X gage: PD tolerance (in.)	0.00030
X gage: PD equivalent of pitch/flank tol. (in.)	0.0009
Z plain gage tolerance (in.)	0.00010
GO gage PD limit (in.)	0.4700
NOT GO gage PD limit (in.)	0.4756
NOT GO crest/minor truncated dia (in.)	0.4931
Root relief width GO (0.167P) (in.)	0.008350
Root relief width NOT GO (0.25P) (in.)	0.012500
Check against formulas	OK
Notes	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.