WEEZMODS BUILD GUIDES

NH34 GMT Build Guide: Dial Sizes, Hands & Case Fit

You can reuse some NH35 parts in an NH34 GMT build, but the extra 24-hour hand changes the space you need at the dial centre and under the crystal. The usual mistake is buying a case and dial because both say “NH compatible”, then finding that the dial will not seat or the seconds hand touches the glass.

Use the measurements, shopping examples and fault checks below to plan a GMT watch before ordering parts. Start with the case specification, then match the dial and complete hand stack to that case.

NH35 to NH34 conversion: the short answer

Standard NH35 hour, minute and seconds hands share the NH34 fitting sizes. You still need an NH34 GMT hand, a dial with GMT centre clearance, and a case/crystal combination that accommodates all four hands.

Choose a fresh GMT build or an NH35 conversion

For a first GMT project, compare the cost of a case and dial sold for NH34 with the work required to reuse your existing parts. A conversion can involve dial modification, a different crystal and extra hand-setting work.

Starting point	What to establish first	Plan for
Fresh build from loose parts	Choose an NH34-compatible case/crystal combination and its specified dial size	All four hands, movement, dial and the components excluded from the case bundle
Existing NH35 watch	Identify your current case, dial and crystal compatibility before buying NH34 Movement	Dial assessment, GMT hand, clearance changes and refitting
Existing GMT watch	Identify its movement and case reference; record the parts you want to keep	Replacement-part checks against that reference

Write down the intended change before shopping: adding a functional second time zone, changing the dial, or creating a particular style. If you only want a different colour scheme, compare a cosmetic mod with the work of changing the movement.

NH34 dimensions and hand sizes

TMI's NH34A drawing specifies a 28.5mm dial, 2.88mm centre opening (+0.05/−0mm) and 0.40mm dial thickness (±0.04mm). These are drawing dimensions for that design, not a guarantee that every aftermarket case accepts the same dial.

Nominal hand-hole sizes in TMI's NH34A Hands drawing

Hand	Bore	Buying implication
Hour	1.50mm	Same nominal size as NH35A
Minute	0.88mm	Same nominal size as NH35A
Seconds	0.198mm	Often sold under the rounded 0.20mm label
GMT / 24-hour	2.20mm	Buy a hand specified for NH34/4R34

The drawing includes manufacturing tolerances; these nominal bores are reference values, not instructions to drill or resize hands. Confirm NH34 compatibility on the supplier's exact handset.

Both movement bodies measure 5.32mm high. In the standard Type M hand-fitting drawings, the seconds post reaches 2.31mm above the dial seat on NH34A versus 1.91mm on NH35A. That 0.40mm difference explains why movement-body height alone cannot confirm crystal clearance. See the TMI NH34A drawings and NH35A drawings.

Dial compatibility: centre hole, feet and date window

28.5mm describes the outside, not the centre opening

When you shop for a dial, record its outer diameter and GMT compatibility as separate entries. A 28.5mm three-hand dial can have the right outside measurement and still fail to clear the NH34 centre assembly. Choose an NH34/4R34 dial for a first GMT build, or arrange an assessment before converting a donor dial.

When it comes to watch modding, flexibility is key. Suppliers often specify dial compatibility for either the NH34 or NH35 movement, but this does not necessarily mean your options are limited.

NH35-compatible dials can be modified to accommodate the NH34 GMT movement, as the NH34 requires a larger centre opening to accommodate its additional GMT hand.

At WEEZMODS, we offer a Dial Centre Enlargement Service for suitable dials. This precision modification enlarges the dial's centre opening while preserving its original outer diameter, allowing greater flexibility when selecting dials for your custom GMT build.

Please note: This conversion works in one direction only. NH35 dials can be modified for NH34 compatibility, but NH34 dials cannot be converted back to their original NH35 centre-opening dimensions.

Crown position and date position are different checks

“3:80” is a crown-position label used in WEEZMODS listings. It does not describe a clock time or the position of the date window. Compare the case's crown position with the dial-foot arrangement, then check the window and numeral orientation against the movement's date disc.

For a specific example, the SSK017 OEM GMT dial lists a 28.5mm diameter, 3:80 crown-position feet and NH34 compatibility. Those details give you three useful checks before purchase. They do not establish fit in an unrelated case. Check the product page for current availability.

For a donor dial, photograph the back and confirm the feet you intend to retain before cutting. Include dial thickness and raised-marker height in your clearance check: the GMT hand passes closest to the face. Centre enlargement will not solve a hand that catches a tall index.

Does an NH34 need a double-dome crystal?

Choose a case and crystal that the supplier specifies for the NH34 hand stack. A double-dome crystal is one common way to provide clearance, while a purpose-designed GMT case can provide enough room beneath a flat crystal. You cannot decide this from “flat” or “domed” alone.

For an SKX007/009 or SRPD-based project, WEEZMODS lists its double-dome sapphire with no bevel edge as NH34 compatible. The listing specifies a 31.5mm bottom chamfer, 30.4mm top chamfer and 5.5mm overall height, includes a gasket and recommends a sloped bezel insert.

That 5.5mm figure describes the crystal itself. It is not a measurement of free space above your fitted dial. Confirm the case seat, gasket, bezel and insert pairing before pressing it in.

Choose a 24-hour scale and check the bezel insert

For a clean dial, you can place the 24-hour reference on a compatible chapter ring or bezel. With a fixed scale, read the GMT hand against that scale. If you choose a rotating GMT bezel, understand its reference position before changing it so you do not confuse an offset reading with the time on the dial.

Before attaching an insert, check its fit and align the reference marker with the dial's 12 o'clock position. Inspect the result from above, and follow the supplier's adhesive instructions.

A WEEZMODS parts shortlist you can check

This is a set of documented component examples, not a complete tested build kit. Confirm the chosen case, dial orientation and remaining parts together.

Component	Documented example	Check before ordering
Movement	NH34A, 3:00 & 3:80 listing: hacking, hand winding; stem, dial washer and installed grey spacer included	Case orientation, date-disc layout and regulation option
Dial	SSK017 OEM dial: 28.5mm, 3:80 feet, NH34 listed	Case dial seat, feet and date-window alignment
GMT hand	Orange GMT hand: 8mm, non-luminous, NH34/4R34	Length against markers; other three hands sold separately
Crystal	SKX007/SRPD no-bevel double dome: NH34 listed, gasket included	Exact case application, bezel and insert profile
Dial conversion	Centre enlargement service: suitable dials only; dial and movement excluded	Assessment before modifying your donor dial

The above list indicated are for reference and not exhaustive.

Assembly checks and common NH34 build faults

Use a clean work area, a movement holder and hand-setting tools suited to the movement. TMI recommends a movement holder and suitable equipment for hand installation. Check calendar changeover before aligning the time hands. Keep the dial washer and follow the orientation shown in the NH3 technical guide.

The NH34 assembly drawing shows the stack from the dial upward as GMT, hour, minute, seconds. Establish the movement's calendar reference before fitting the hands, align the time indications, then advance them with the crown and inspect the gaps from the side. Check for contact across the full dial and at overlapping hand positions before closing the case.

Symptom	Checks to make	Next step
Dial will not sit flat	Centre opening, feet, underside protrusions and washer seating	Stop pressing; have the dial fit assessed
GMT hand catches near markers	Raised indices, hand level and height above the dial	Recheck the dial/hand pairing and hand setting
Watch runs uncased but stops when closed	Hand-to-crystal contact, caseback pressure and movement seating	Reopen and inspect clearances; do not tighten harder
Date appears off-centre or tilted	Dial orientation, window location and date-disc version	Confirm the exact dial/movement combination
Crown resists seating	Stem length, movement seating and stem alignment	Check fit before further stem trimming

These are diagnostic checks, not proof of a single cause. If parts bind or a hand will not seat with normal technique, stop and have an experienced assembler inspect them. Do not force the assembly to compensate for incompatible parts.

How to read and set an NH34 GMT watch

The GMT hand uses a 24-hour scale: 14 means 2 p.m. in the second time zone. If your local hour and minute hands show 10:00 while the GMT hand points to 14, you can read local time as 10 a.m. and the second zone as 2 p.m. A 12-hour dive insert alone will not give you that direct 24-hour reading.

The NH34 uses an adjustable GMT hand, often called a caller GMT. To set the main time, pull the crown to the second click. At the first click, TMI specifies turning left to correct the date and right to adjust the 24-hour hand. Push the crown back after setting, and secure a screw-down crown according to the case instructions.

Keep quick date correction outside 9 p.m. to 4 a.m. TMI identifies that interval as a malfunction risk. If you are unsure of the watch's AM/PM state, move the main hands to a time outside that interval before correcting the date. Use the TMI operation manual for the movement's setting procedure.

NH34 build FAQs

Can I keep my NH35 handset?

Yes. The nominal hour, minute and seconds bores match between NH35 and NH34. Add an NH34-compatible GMT hand and confirm clearance in your chosen case.

Can I enlarge the dial myself?

Yes, you may enlarge the dial hole size for NH34/4R34 Movement. However, such modification is irreversible and may damage the finish if done incorrectly. A purpose-made GMT dial is a simpler first-build choice for beginners.

Will a GMT bezel make my NH35 a GMT watch?

No. You need a movement that drives the additional time indication and its matching GMT hand. The bezel supplies the reading scale.

Should I buy the crystal before choosing the case?

Choose the case first, then select the specified crystal and gasket. For an existing case, identify its reference and current crystal dimensions before buying a replacement.