1 UNM × 0.25 UNM profile External Thread Specifications

1.00 UNM External

ASMESTD: ASME B1.10MSOURCE: Tables 1, 2, 4 (external)TYPE: External (bolt/screw)CLASS: Only class (zero allowance)SERIES: Unified MiniaturePreferred (bold)
Major diameter
1.000 – 0.964
max – min
Pitch diameter
0.838 – 0.810
max – min
Root diameter d3
0.714 – 0.666
max – min (min is a reference value)
Design root radius R
0.046
Table 4

Thread profile

1.00 UNM External: external MJ profile with its tolerance zone, drawn to scaled = 1.000d2 = 0.838d1 = 0.760P = 0.2560°30°crest 0.031250root R 0.046 – 0.046Major dia zone (crest)1.000 – 0.964 Td 0.036Pitch dia zone (flanks)0.838 – 0.810 Td2 0.028Root zone d3 (radius R)0.714 – 0.666Fundamental deviationes = 0, position H/80.0270633H/80.081190H/40.054127h = 5H/80.120000H0.216506thread axis, 0.500 mm below the major radius (diameters shortened)MALE · external thread · 1.00 UNM External

1.00 UNM External: 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
Major diameter dCrest of the screw: maximum is the basic major diameter (zero allowance)1.0001.0000.9640.036
Pitch diameter d2Sets the fit0.8380.8380.8100.028
Minor diameter d3Bottom of the root radius: maximum is the design minor diameter; the minimum is for tool design0.7600.7140.666ref.0.048ref.
Design root radius RTable 40.046
Allowance esZero 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 0.000ei −0.028male pitch dia Only class (zero allowance)des 0.000ei −0.036male major 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 minor dia min of an external thread is used in the design of tools; diameter acceptance is generally based on maximum material gaging. The external minor dia tolerance is not printed in Table 2; the value shown is Table 6 (0.1600P + 0.008). Table 1 heads the d3 column "1.145185P"; the printed values follow 1.1451815P (Tables 3 and 5). 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 External screws into a thread of the same standard at the same size and pitch. The standard mating internal 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 internal
All values for 1.00 UNM Externalevery column of the workbook row
All values of the workbook row 1.00 UNM External
Designation1.00 UNM External
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 / internalExternal
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 (external)
Printed page2, 3, 6
Major dia max (mm)1.000
Major dia min (mm)0.964
Major dia tolerance (mm)0.036
Allowance es / EI (mm)0.000
Major dia statusToleranced: max = basic major dia (zero allowance), tolerance minus
Basic pitch dia D2 (mm)0.838
Pitch dia max (mm)0.838
Pitch dia min (mm)0.810
PD tolerance (mm)0.028
Basic minor dia D1 (mm)0.760
Minor dia max (mm)0.714
Minor dia min (mm)0.666
Minor dia tolerance (mm)0.048
Minor dia statusMax = design minor dia d3 (maximum material); min is for tool design (Table 2 note 1)
Design root radius, Table 4 (mm)0.046
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)0.031250
Root flat (mm)none (radiused root)
Root radius for model (mm)0.046295
Design thread height (mm)0.143148
Sweep cut: start diameter (mm)1.000000
Sweep cut: tip diameter (mm)0.713705
Sweep cut: depth (mm)0.143148
Sweep cut: profile width at start diameter (mm)0.218750
Crest flat as modelled (mm)0.031250
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 minor dia min of an external thread is used in the design of tools; diameter acceptance is generally based on maximum material gaging. The external minor dia tolerance is not printed in Table 2; the value shown is Table 6 (0.1600P + 0.008). Table 1 heads the d3 column "1.145185P"; the printed values follow 1.1451815P (Tables 3 and 5). 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.