Quick answer
Reference 1558420 is the Jaeger-LeCoultre Master Ultra Thin Moon 39. The original is a 39 mm stainless steel watch with a silvered grained dial, a moon phase at 6 o'clock, and a date pointer on the same subdial. Replica versions sell in three tiers: quartz, basic automatic, and high grade automatic with a working moon phase. Prices sit between $80 and $450. The moon phase is the part to inspect first, because many replicas swap the 29.5 day lunar disc for a 24 hour sun and moon disc.
What the reference is
Jaeger-LeCoultre released the Master Ultra Thin Moon in a 39 mm case. Reference 1558420 covers the stainless steel version with a silvered, grained dial. The case measures about 9.9 mm thick. Lugs taper, the case sides are polished, and the bezel is thin.
Reported specifications
- Case: 39 mm stainless steel, thickness about 9.9 mm
- Movement: calibre 925/1, automatic, 28,800 vph
- Power reserve: listings show 38 to 43 hours
- Functions: hours, minutes, moon phase, date by pointer
- Crystal: sapphire front and back, display caseback
- Water resistance: 5 bar, 50 m
- Strap: leather with a steel pin buckle
Published material differs on the seconds hand. Photos of the reference show no central sweep second in the common layout. Match the sample photo to the seller photo on this point before you order.
How replicas of 1558420 differ
Replica makers copy the case shape and the dial layout. The internal difference decides the price.
Tier 1: quartz
A quartz module drives the hands. The moon phase is a printed disc or a static aperture. The caseback holds an engraved plate, not a movement. Case thickness runs 10.5 mm to 11.5 mm, which is 1 mm to 2 mm more than the original.
Tier 2: basic automatic
A Miyota 9015, Seagull, or similar automatic movement sits inside. The moon phase disc turns once per 24 hours, so the moon sits in the aperture during the day and leaves at night. The date hand moves, but the drop at midnight can be off by hours.
Tier 3: high grade automatic
These builds use a moon phase module on top of an automatic base, so the disc advances about every 29.5 days. The rotor carries decoration, the dial print has cleaner edges, and the case profile sits near 9.9 mm. Price lands at the top of the range.
QC checklist
- Measure case diameter and thickness with calipers. Expect 39 mm and 10 mm or more.
- Watch the moon phase aperture for two days. A 29.5 day disc moves about 1 mm per day. A 24 hour disc crosses the aperture in half a day.
- Check the date pointer at midnight for three nights. It should land on the new number each time.
- Read the dial print. The maker name uses a hyphen. Copy the exact text from the product photo.
- Check crown action and winding feel. Grit means a dry or damaged keyless works.
- Look for dust under the crystal and misaligned markers.
- Confirm lug width and strap length before you order a spare strap.
Price range
- Quartz: $80 to $150
- Basic automatic: $150 to $260
- High grade automatic with working moon phase: $260 to $450
Prices move with the seller, the strap, and the currency. The numbers above are asking prices, not sale prices.
What a replica cannot copy
The calibre 925/1 uses finishing a replica movement does not match: Cotes de Geneve stripes, blued screws, and a hand-finished rotor. Rate stability over a week is another gap. A base automatic holds a few seconds a day in the first month, then drifts as lubricant spreads. Service for the original comes from a JLC boutique. Replica parts come from the seller or a local watchmaker.
Care
Keep water away from any replica unless the listing states a tested rating. The case gasket on a $200 watch is the weak point. Wipe the strap, store the watch flat, and set the moon phase with the crown position listed in the seller manual, not by pushing the disc.