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Movement · TMI (Seiko Instruments) · automatic

TMI NH38 movement

TMI NH38 is an automatic movement by TMI (Seiko Instruments): 27.4 mm1 across, 5.32 mm1 high, beating at 21,600 bph2.

Sources checked · How we source numbers
TMI NH38: movement drawingTMI NH38, dial side, to scale: movement diameter 27.4 mm; casing diameter 29.36 mm; size 12‴; height 5.32 mm; hour, minute, second hand hole Ø — (unknown).movement Ø 27.4casing Ø 29.3612‴ as printed · Ø 27.4 = 12.15‴5.32SIDE · SECTION · height 5.32Ahour, minute, second hand hole Ø —DETAIL A · 10:1
TMI NH38, dial sideDrawing from data, not a photo · mm

NH38 at a glance

Diameter
27.4 mm1
Height
5.32 mm1
Beat rate
21,600 bph2

New to the terms? Read quartz vs automatic or watch movement types.

Setting and servicing the NH38

The figures a watchmaker or a timegrapher needs for the NH38, as TMI prints them.

Hacking seconds
Yes2
Hand winding
Yes4

What fits the NH38

The figures a dial, hands or case must match for the NH38, as TMI prints them.

Casing diameter
29.36 mm1

What can replace the NH38

11 calibres of the Seiko NH / 4R / 7S group checked against the NH38: diameter, height, hand holes, date window, crown and dial feet. A verdict marked “not confirmed” lacks one of those figures for the NH38 or the other calibre.

Not published, so not checked in several comparisons:

  • hand holes for NH38, NH39, NH70, NH72, 4R35, 4R34 and 4R36
  • crown position for NH38, NH39, NH70, NH72, 4R35, 4R34 and 4R36
  • dial feet for NH38, NH39, NH70, NH72, 4R35, 4R34 and 4R36

  1. NH38 → NH39

    Drop-in· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • =heightSame height: 5.32 mm.

  2. NH38 → NH70

    Drop-in· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • =heightSame height: 5.32 mm.

  3. NH38 → NH72

    Drop-in· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • =heightSame height: 5.32 mm.

  4. NH38 → 4R35

    Fits with changes· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • =heightSame height: 5.32 mm.
    • ≠date4R35 has a date: a dial without a window hides it, and the crown gets a date-setting step.

  5. NH38 → NH35

    Fits with changes· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • =heightSame height: 5.32 mm.
    • ≠dateNH35 has a date: a dial without a window hides it, and the crown gets a date-setting step.

  6. NH38 → 4R34

    Fits with changes· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • ≠functions4R34 adds a 24-hour hand: it needs a dial and hand set made for it.
    • ≠date4R34 has a date: a dial without a window hides it, and the crown gets a date-setting step.

    Not published, so not checked: height for 4R34.

  7. NH38 → 4R36

    Fits with changes· not confirmed
    • =diameterSame movement diameter: 27.4 mm.
    • =heightSame height: 5.32 mm.
    • ≠date4R36 adds a day wheel: a date-only dial hides it, and the crown gets a day-setting step.
    • ≠date4R36 has a date: a dial without a window hides it, and the crown gets a date-setting step.

  8. NH38 → NH34

    Fits with changes· not confirmed
    • =diameterSame size in lignes: 12‴.
    • =heightSame height: 5.32 mm.
    • ≠functionsNH34 adds a 24-hour hand: it needs a dial and hand set made for it.
    • ≠dateNH34 has a date: a dial without a window hides it, and the crown gets a date-setting step.

    Not published, so not checked: a millimetre diameter for NH34.

3 more calibres in the group fit less well; compare any of them with the movement comparison.

Same family at TMI

How each differs from the NH38, worked out from the figures on its own page.

All NH38 figures

Every figure we hold for the NH38, with its source. Where sources disagree, each value is shown.

Size

Size in lignes
12‴3
Diameter
27.4 mm1
Casing diameter
29.36 mm1
Height
5.32 mm1

Running

Beat rate
21,600 bph2
Hands and functions
hours, minutes, centre seconds2
Hacking seconds
Yes2
Hand winding
Yes4

Not published yet

  • Jewels: not published by TMI
  • Power reserve: not published by TMI
  • Accuracy (maker): not published by TMI
  • Lift angle: not published by TMI
  • Hand holes: only in TMI’s drawing; not read yet
  • Dial feet: only in TMI’s drawing; not read yet
  • Stem part number: not in the documents we read
  • Do not set the date: not published

Versions

NH38A3J · NH38A3M · NH38A3MN · NH38A4J · NH38A4MN[3]

NH38 questions

Does the NH38 hack and hand-wind?

Yes, it hacks: the seconds hand stops with the crown pulled out. It can be wound by the crown.

Source [2][4]

What can replace the NH38?

From the published figures, the closest is the NH39: drop-in, not confirmed for every part, with 2 more in the same group. Same movement diameter: 27.4 mm.

More on movements

Sources

Documents checked · Report a wrong number

  1. 1Time Module Ltd. — TMI Watch Movement Specification and Drawing (Spec Sheet) NH38 · pdf · read
  2. 2Time Module Ltd. — TMI Technical Guide & Parts Catalogue NH38 · pdf · read
  3. 3Time Module Ltd. — Product Code Search, code=NH38 · html · read
  4. 4Time Module Ltd. — TMI Operation Manual NH38 · pdf · read