1 UNM × 0.25 UNM profile Internal Thread Specifications

1.00 UNM Internal

ASMESTD: ASME B1.10MSOURCE: Tables 1, 2, 4 (internal)TYPE: Internal (nut/tapped hole)CLASS: Only class (zero allowance)SERIES: Unified MiniaturePreferred (bold)
Major diameter
1.018 min
max 1.068 (reference)
Pitch diameter
0.838 – 0.866
min – max
Minor diameter
0.760 – 0.852
min – max
Pitch
0.25
mm

Thread profile

1.00 UNM Internal: internal M profile with its tolerance zone, drawn to scaleD = 1.000D2 = 0.838D1 = 0.760P = 0.2560°30°crest 0.080186root R 0.018000Major dia (root)1.018 min (1.068 max ref.)Pitch dia zone (flanks)0.838 – 0.866 TD2 0.028Minor dia zone (crests)0.760 – 0.852 TD1 0.092Fundamental deviationEI = 0, position HH/80.0270633H/80.081190H/40.054127h = 5H/80.120000H0.216506thread axis, 0.500 mm below the major radius (diameters shortened)FEMALE · internal thread · 1.00 UNM Internal

1.00 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 diameter0.7600.8520.7600.092
Pitch diameter D2Sets the fit0.8380.8660.8380.028
Major diameter DRoot of the nut: minimum is the design major diameter; the maximum is for tool design1.0001.068ref.1.0180.050ref.
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 +0.028EI 0.000female pitch diaD1ES +0.092EI 0.000female minor dia (crest)

Engagement, mating clearances and gaging

Length of engagement Table 1

Minimum, 2/3 D
0.6667 mm
Maximum, 1.5 D
1.5000 mm

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

Major diameter
0.018 / 0.104 mm
Pitch diameter
0.000 / 0.056 mm
Minor diameter
0.046 / 0.186 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
1.00 UNM101.60.03940.0330.02810.02990.04015260.00062OK

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
1.00 UNM101.60.03940.0380.00140.0330.03190.00110.02810.02620.02990.03350.00360.0330.03410.00110.04010.042OK

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

1.00 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

→ 0.90 UNM→ 1.10 UNM→ 1 UNM × 0.25 external
All values for 1.00 UNM Internalevery column of the workbook row
All values of the workbook row 1.00 UNM Internal
Designation1.00 UNM Internal
Standard designation (para. 1.3)1.00 UNM
Threads per inch n (Table B1)101.6
Thread formUNM
Series (Table 1)UNM
Series nameUnified Miniature
External / internalInternal
ClassOnly class (zero allowance)
Nominal size (mm)1.00
Pitch P (mm)0.250
Basic major dia D (mm)1.000
Size categoryPreferred (bold)
Source tableTables 1, 2, 4 (internal)
Printed page2, 3, 6
Major dia max (mm)1.068
Major dia min (mm)1.018
Major dia tolerance (mm)0.050
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)0.838
Pitch dia max (mm)0.866
Pitch dia min (mm)0.838
PD tolerance (mm)0.028
Basic minor dia D1 (mm)0.760
Minor dia max (mm)0.852
Minor dia min (mm)0.760
Minor dia tolerance (mm)0.092
Minor dia statusToleranced, tolerance plus; gaged with GO / NOT GO plain plug gages (para. 1.5.2)
Design root radius, Table 4 (mm)0.018
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)5.4271
Lead angle (deg min)5° 26′
Lead angle printed (Table 1)5° 26′
Sectional area at minor dia (sq mm)0.400
Sectional area printed (Table 1) (sq mm)0.400
Thread angle (deg)60
Flank angle (deg)30
Sharp V height H (mm)0.216506
Thread height h = 0.48P (mm)0.120000
Addendum of external thread 0.375H (mm)0.081190
Crest flat (mm)0.080186
Root flat (mm)none (radiused root)
Root radius for model (mm)0.018042
Design thread height (mm)0.129021
Sweep cut: start diameter (mm)0.760000
Sweep cut: tip diameter (mm)1.018042
Sweep cut: depth (mm)0.129021
Sweep cut: profile width at start diameter (mm)0.169814
Crest flat as modelled (mm)0.080186
Tapernone: parallel thread
Gauge dimensionsnot given in the standard (App. A)
Length of engagement min = 2/3 D (mm)0.6667
Length of engagement max = 1.5 D (mm)1.5000
Same-size mate: major dia clearance, tightest (mm)0.018
Same-size mate: major dia clearance, loosest (mm)0.104
Same-size mate: pitch dia clearance, tightest (mm)0.000
Same-size mate: pitch dia clearance, loosest (mm)0.056
Same-size mate: minor dia clearance, tightest (mm)0.046
Same-size mate: minor dia clearance, loosest (mm)0.186
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.