0.55 UNM × 0.125 UNM profile Internal Thread Specifications

0.55 UNM Internal

ASMESTD: ASME B1.10MSOURCE: Tables 1, 2, 4 (internal)TYPE: Internal (nut/tapped hole)CLASS: Only class (zero allowance)SERIES: Unified MiniatureOther
Major diameter
0.559 min
max 0.588 (reference)
Pitch diameter
0.469 – 0.487
min – max
Minor diameter
0.430 – 0.482
min – max
Pitch
0.125
mm

Thread profile

0.55 UNM Internal: internal M profile with its tolerance zone, drawn to scaleD = 0.550D2 = 0.469D1 = 0.430P = 0.12560°30°crest 0.040093root R 0.009000Major dia (root)0.559 min (0.588 max ref.)Pitch dia zone (flanks)0.469 – 0.487 TD2 0.018Minor dia zone (crests)0.430 – 0.482 TD1 0.052Fundamental deviationEI = 0, position HH/80.0135323H/80.040595H/40.027063h = 5H/80.060000H0.108253thread axis, 0.275 mm below the major radius (diameters shortened)FEMALE · internal thread · 0.55 UNM Internal

0.55 UNM Internal: solid line = maximum material profile, dashed = minimum material, hatched = tolerance zone, grey dashed = basic profile. Drawn to scale; values in mm, diameters shortened.

Limits of size

DimensionBasicMaxMinTolerance
Minor diameter D1Crest of the nut: minimum is the basic minor diameter0.4300.4820.4300.052
Pitch diameter D2Sets the fit0.4690.4870.4690.018
Major diameter DRoot of the nut: minimum is the design major diameter; the maximum is for tool design0.5500.588ref.0.5590.029ref.
Allowance EIZero allowance on all diameters0.000

Dimensions in millimetres. Values are those of the standard (ASME B1.10M); 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.

Tolerance zones relative to the basic size, mm

Tolerance zones relative to the basic sizezero line = basic size+ above · − belowD2ES +0.018EI 0.000female pitch diaD1ES +0.052EI 0.000female minor dia (crest)

Engagement, mating clearances and gaging

Length of engagement Table 1

Minimum, 2/3 D
0.3667 mm
Maximum, 1.5 D
0.8250 mm

Same-size mate: clearance at the limits tightest / loosest

Major diameter
0.009 / 0.059 mm
Pitch diameter
0.000 / 0.036 mm
Minor diameter
0.023 / 0.103 mm

Lead, flank and gaging

Lead variation ±δP
not given in the standard mm
Equivalent change in functional diameter δd2
not given in the standard mm
Half-angle variation ±δα
not given in the standard
Gage dimensions
not given in the standard (App. A)

Inch values nonmandatory appendices, as printed

Table B1: inch conversion of Table 1 (nonmandatory appendix)

Size designationThreads/in. nD, d (in.)D2, d2 (in.)d3 (in.)D1 internal (in.)D internal (in.)Lead angle degLead angle minSectional area (sq in.)Check against Table 1 / 25.4
0.55 UNM203.20.02170.01850.0160.01690.0224510.0002015OK

Table C1: inch conversion of Table 2 (nonmandatory appendix)

Size designationThreads/in. nExternal major dia · MaxExternal major dia · MinExternal major dia · TolExternal pitch dia · MaxExternal pitch dia · MinExternal pitch dia · TolExternal minor dia · MaxExternal minor dia · Min [Note 1]Internal minor dia · MinInternal minor dia · MaxInternal minor dia · TolInternal pitch dia · MinInternal pitch dia · MaxInternal pitch dia · TolInternal major dia · MinInternal major dia · Max [Note 1]Internal major dia · Check against Table 2 / 25.4
0.55 UNM203.20.02170.02080.00080.01850.01780.00070.0160.01490.01690.0190.0020.01850.01920.00070.0220.0231OK

Notes

  • Table 2 note (1): the major dia max of an internal thread is used in the design of tools; diameter acceptance is generally based on maximum material gaging. The internal major dia tolerance is not printed in Table 2; the value shown is Table 6 (0.1680P + 0.008). Full limits of minor dia normally apply to internal threads (para. 1.3); otherwise the designation is supplemented by the minor dia limits. Single class with zero allowance on all diameters (para. 2.6); single start (para. 2.4); parallel thread; reference temperature 20 deg C (para. 1.5.3).

Mates

0.55 UNM Internal takes a thread of the same standard at the same size and pitch. The standard mating external thread is class UNM. 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

→ 0.50 UNM→ 0.60 UNM→ 0.55 UNM × 0.125 external
All values for 0.55 UNM Internalevery column of the workbook row
All values of the workbook row 0.55 UNM Internal
Designation0.55 UNM Internal
Standard designation (para. 1.3)0.55 UNM
Threads per inch n (Table B1)203.2
Thread formUNM
Series (Table 1)UNM
Series nameUnified Miniature
External / internalInternal
ClassOnly class (zero allowance)
Nominal size (mm)0.55
Pitch P (mm)0.125
Basic major dia D (mm)0.550
Size categoryOther
Source tableTables 1, 2, 4 (internal)
Printed page2, 3, 6
Major dia max (mm)0.588
Major dia min (mm)0.559
Major dia tolerance (mm)0.029
Allowance es / EI (mm)0.000
Major dia statusMin = design major dia D + 0.0721688P; max is for tool design (Table 2 note 1)
Basic pitch dia D2 (mm)0.469
Pitch dia max (mm)0.487
Pitch dia min (mm)0.469
PD tolerance (mm)0.018
Basic minor dia D1 (mm)0.430
Minor dia max (mm)0.482
Minor dia min (mm)0.430
Minor dia tolerance (mm)0.052
Minor dia statusToleranced, tolerance plus; gaged with GO / NOT GO plain plug gages (para. 1.5.2)
Design root radius, Table 4 (mm)0.009
Lead variation ± (mm)not given in the standard
Equivalent change in functional dia (mm)not given in the standard
Half-angle variation ±not given in the standard
Lead angle at basic PD (deg)4.8512
Lead angle (deg min)4° 51′
Lead angle printed (Table 1)4° 51′
Sectional area at minor dia (sq mm)0.130
Sectional area printed (Table 1) (sq mm)0.130
Thread angle (deg)60
Flank angle (deg)30
Sharp V height H (mm)0.108253
Thread height h = 0.48P (mm)0.060000
Addendum of external thread 0.375H (mm)0.040595
Crest flat (mm)0.040093
Root flat (mm)none (radiused root)
Root radius for model (mm)0.009021
Design thread height (mm)0.064511
Sweep cut: start diameter (mm)0.430000
Sweep cut: tip diameter (mm)0.559021
Sweep cut: depth (mm)0.064511
Sweep cut: profile width at start diameter (mm)0.084907
Crest flat as modelled (mm)0.040093
Tapernone: parallel thread
Gauge dimensionsnot given in the standard (App. A)
Length of engagement min = 2/3 D (mm)0.3667
Length of engagement max = 1.5 D (mm)0.8250
Same-size mate: major dia clearance, tightest (mm)0.009
Same-size mate: major dia clearance, loosest (mm)0.059
Same-size mate: pitch dia clearance, tightest (mm)0.000
Same-size mate: pitch dia clearance, loosest (mm)0.036
Same-size mate: minor dia clearance, tightest (mm)0.023
Same-size mate: minor dia clearance, loosest (mm)0.103
Check against formulasOK: the printed limits, tolerances and design sizes of this row agree with the formulas of Tables 5 and 6 (rounded to 3 places), and Table 1 lead angle and sectional area with their formulas.
NotesTable 2 note (1): the major dia max of an internal thread is used in the design of tools; diameter acceptance is generally based on maximum material gaging. The internal major dia tolerance is not printed in Table 2; the value shown is Table 6 (0.1680P + 0.008). Full limits of minor dia normally apply to internal threads (para. 1.3); otherwise the designation is supplemented by the minor dia limits. Single class with zero allowance on all diameters (para. 2.6); single start (para. 2.4); parallel thread; reference temperature 20 deg C (para. 1.5.3).

Related tools

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