MJ20 × 2.5 MJ profile Internal Thread Specifications
MJ20 x 2.5 - 4H5H
ASMESTD: ASME B1.21MSOURCE: Table 7 · p. 25TYPE: Internal (nut/tapped hole)CLASS: 4H5HSERIES: Coarse pitchAerospace class, no allowance (approx. inch Class 3B)1st choice (Col. 1)
Major diameter
20.000 min
max 20.501 (reference)
Pitch diameter
18.376 – 18.516
min – max
Minor diameter
17.564 – 17.919
min – max
Pitch
2.5
mm
Thread profile
MJ20 x 2.5 - 4H5H: 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, class 4H5H
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter DRoot of the nut; max for reference | 20.000 | 20.501ref. | 20.000 | 0.501 |
| Pitch diameter D2Sets the fit | 18.37620 | 18.516 | 18.376 | 0.140 |
| Minor diameter D1Nut crest; clears the bolt root radius | 17.56430 | 17.919 | 17.564 | 0.355 |
| Allowance EISpace for coating | 0.000 |
Dimensions in millimetres. Values are those of the standard (ASME B1.21M); 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
Lead, flank angle and length of engagement
- Allowable lead variation ±δP
- 0.0404 mmBetween any two points within the GO gage length
- Equivalent change in functional diameter δd2
- 0.0700 mmHalf the pitch diameter tolerance
- Allowable half-angle variation ±δα
- 0° 50′ Each 30° flank
- Cumulative form variation
- 0.0700 mmWhen specified for H/h: 0.5 × PD tolerance (para. 4.4.1)
- Runout of major/minor to pitch cylinder FIM
- 0.140 mmMax FIM when measured (para. 4.4.3)
- Length of engagement, normal upper limit LE
- 30.000 mmTable 12 / 13 allow the tolerance for this range
Lead source: Table 12, p. 45; half-angle source: Table 13, p. 50
MJ root radius and minor diameter paras. 1.1, 2.4.2, Fig. 4
- Coating allowance, pitch diameter
- 0.038 mm
- Coating allowance, major and minor diameter
- 0.019 mm
Notes
- MJ internal minor dia D1 min 17.564 mm = D min - 9/8H: raised above the M profile to clear the external root radius (para. 1.1). No root radius is specified; the root may not transgress the basic profile (para. 2.4.1). MJ internal threads accept ASME B1.13M (M profile) external threads, but an MJ external thread may interfere with an M internal thread minor dia (para. 1.3).
Mates
MJ20 x 2.5 - 4H5H takes a thread of the same standard at the same size and pitch. The standard mating external thread is class 4h6h. 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
All values for MJ20 x 2.5 - 4H5Hevery column of the workbook row
| Designation | MJ20 x 2.5 - 4H5H |
|---|---|
| Alternate designation | MJ20x2.5-4H5H |
| Pitch (mm) | 2.50 |
| Thread form | MJ |
| Series (Table 2) | Coarse |
| Series name | Coarse pitch |
| External / internal | Internal |
| Class | 4H5H |
| Nominal size (mm) | 20 |
| Pitch P (mm) | 2.50 |
| Basic major dia D, d (mm) | 20.000 |
| Size category | 1st choice (Col. 1) |
| Source table | Table 7 |
| Printed page | 25 |
| Major dia max (mm) | 20.501 |
| Major dia min (mm) | 20.000 |
| Major dia tolerance (mm) | 0.501 |
| PD tolerance LE basis | 1D |
| LE for PD tolerance (mm) | 20.000 |
| Allowance es / EI (mm) | 0.000 |
| Major dia status | Min toleranced; max = D2 max + 11/12H (para. 4.3.2) |
| Basic pitch dia D2, d2 (mm) | 18.37620 |
| Pitch dia max (mm) | 18.516 |
| Pitch dia min (mm) | 18.376 |
| PD tolerance (mm) | 0.140 |
| Basic minor dia D1, d1 (mm) | 17.56430 |
| Minor dia max (mm) | 17.919 |
| Minor dia min (mm) | 17.564 |
| Minor dia tolerance (mm) | 0.355 |
| Minor dia status | Toleranced (TD1 grade 5, Table 10) |
| Root radius max (mm) | none specified |
| Root radius min (mm) | none specified |
| Lead variation ± (mm) | 0.0404 |
| Equivalent change in functional dia (mm) | 0.0700 |
| Lead values source | Table 12, p. 45 |
| Half-angle variation ± | 0° 50′ |
| Half-angle source | Table 13, p. 50 |
| Lead angle at basic PD (deg) | 2.4796 |
| Lead angle (deg min) | 2° 29′ |
| Tensile stress area As (mm²) | not given in the standard |
| Thread angle (deg) | 60 |
| Flank angle (deg) | 30 |
| Sharp V height H (mm) | 2.16506 |
| Thread height h (mm) | 1.21785 |
| Crest flat (mm) | 0.78125 |
| Root flat (mm) | 0.31250 |
| Root radius for model (mm) | none specified |
| Sweep cut: start diameter (mm) | 17.564 |
| Sweep cut: tip diameter (mm) | 20.000 |
| Sweep cut: depth (mm) | 1.21800 |
| Sweep cut: profile width at start diameter (mm) | 1.71875 |
| Crest flat as modelled (mm) | 0.78125 |
| Normal LE upper limit (mm) | 30.000 |
| PD tolerance, LE over 1.5D/15P to 3D/30P (×1.25) (mm) | 0.175 |
| PD tolerance, LE over 3D/30P (×1.5) (mm) | 0.210 |
| Cumulative form variation 0.5×PD tol (mm) | 0.0700 |
| Runout max FIM = PD tol (mm) | 0.140 |
| Coating allowance, pitch dia (mm) | 0.038 |
| Coating allowance, major and minor dia (mm) | 0.019 |
| Table 5 other preferred | Yes |
| Listed in ISO 261 | Yes |
| Class use | Aerospace class, no allowance (approx. inch Class 3B) |
| Check against formulas | OK |
| Notes | MJ internal minor dia D1 min 17.564 mm = D min - 9/8H: raised above the M profile to clear the external root radius (para. 1.1). No root radius is specified; the root may not transgress the basic profile (para. 2.4.1). MJ internal threads accept ASME B1.13M (M profile) external threads, but an MJ external thread may interfere with an M internal thread minor dia (para. 1.3). |
| PD tolerance grade | 4 |
| Tolerance position | H |
| Allowable taper (mm), para. 4.4.4 | 0.140 |
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ASME B1.21M: Metric Screw Threads: MJ Profile. Source: workbook data (2026-10-11). Confirm against your licensed copy of the standard before use.