NH35 vs NH35A: Which Movement Should You Pick?

NH35 vs NH35A comes down to who made the movement: the NH35A is the Seiko Instruments (TMI) caliber, while many movements sold as "NH35" today are compatible copies built to the same size and layout. This guide explains what is the same, what differs and which one to choose for your build.

Both are offered in our Prodi Dive Kit: $349 with the standard movement, $449 with the Japanese NH35A.

What is the difference between the NH35 and the NH35A?

On paper, NH35 and NH35A name the same Seiko caliber; Caliber Corner lists them as one movement. In the market, "NH35" is also used for compatible movements made by other factories, so the real question is Seiko TMI versus compatible.

Seiko sells this caliber to other watch brands through its TMI division. It is described as an unbranded version of the Seiko 4R35, the movement inside many Seiko watches. Because it is so popular with builders and modders, other factories now make movements with the same footprint, so a compatible movement fits the same dials, hands and cases.

The Seiko TMI option

Japanese Automatic Movement · Seiko TMI NH35A

$269 on its own · $449 as a full kit

24 jewels · 21,600 bph · about 41 h power reserve · hacking · hand-winding · date

Use code WELCOME for 10% off your order.

See the movement

What are the NH35A specifications?

Seiko's NH35A has 24 jewels, beats at 21,600 vibrations per hour, holds about 41 hours of power reserve and is rated at -20 to +40 seconds per day.

• Jewels: 24
• Beat rate: 21,600 bph (3 Hz)
• Power reserve: about 41 hours
• Functions: hours, minutes, hacking seconds, quickset date
• Winding: automatic, plus hand-winding through the crown
• Movement size: 27.4 mm across, 5.32 mm tall

How accurate are they?

Seiko's published range for the NH35A is -20 to +40 seconds per day. Compatible movements do not share one official figure, so accuracy depends on the factory and the batch.

That range is wide on purpose: it covers every position and temperature. On the wrist, many movements run well inside it. If you care most about consistency over years, the NH35A is the safer pick.

How do you tell a Seiko TMI NH35A?

Buy from a seller who names the maker. Rotor markings help but are not proof on their own: Seiko TMI rotors are often stamped Japan or Malaysia, and some recent movements carry no origin marking at all.

This is why we list our two options plainly as "NH35-compatible" and "Seiko TMI NH35A" rather than calling both NH35.

Is the price difference worth it?

For a first practice build, the compatible movement is good value. For a watch you plan to wear daily and keep for years, the extra $100 for the Japanese movement buys the Seiko TMI caliber and its published spec.

• Choose standard ($349) if this is your first build, a gift to try the hobby, or a watch you plan to modify again.
• Choose Japanese ($449) if you want the Seiko TMI movement, plan to have it serviced, or are building a keeper.

Either way, the build is the same. Our guide on picking a watch kit for beginners covers the steps.

Can you swap one for the other later?

Yes. Because they share the same layout, you can move your dial and hands to a new movement later. You will need to fit the crown stem again.

Many builders start with a compatible movement and upgrade once they are confident. Spare movements are also handy if you get into an NH35 mod kit project. You can buy either one separately in our parts and tools collection.

How do you check your movement's accuracy at home?

Set the watch to an accurate time source, check it at the same time each day for a week, and divide the total drift by seven. That gives you seconds per day to compare with the published range.

1. Wind it fully. About 30 turns of the crown, or wear it for a full day first.
2. Set it exactly. Pull the crown to stop the seconds hand at 12, then push it in on the minute of an accurate clock, such as time.gov.
3. Check at the same time daily. Note how many seconds ahead or behind it is.
4. Keep your routine normal. Wear it as you usually would; rest position at night changes the result a little.
5. Work out the average. Total drift after seven days divided by seven is your daily rate.

A rate inside -20 to +40 seconds per day is within the NH35A's published range. A watch that suddenly runs many minutes fast may be magnetized, which is easy to fix with a demagnetizer.

Which one should you pick for your plans?

Match the movement to what the watch is for. Learning and modding favor the standard movement; a daily watch you keep for years favors the NH35A.

The bottom line

In the NH35 vs NH35A question, the movements work the same and fit the same parts; the difference is the maker and the published accuracy. Pick the standard movement to learn, the Japanese NH35A to keep. If you are unsure, ask us and we reply within 24 hours.