The short answer
A fake Aqua Terra 321.10.42.50.01.001 is a copy of the 41.5 mm steel Seamaster Aqua Terra 150M with the black teak dial and the Calibre 8500 inside. Good copies match the case size, the dial texture and the bracelet profile well enough that a photo on a wrist proves nothing. They do not match the movement, and almost every tell you can find in your hand comes back to that one gap.
What the genuine reference is
Before judging a copy, pin down the original. The 321.10.42.50.01.001 uses Omega's 41.5 mm case, not the 38.5 mm one, and it sits on the steel bracelet with polished center links.
- Case: 41.5 mm steel, about 13.2 mm thick, 20 mm lug width, screw-down crown.
- Movement: Calibre 8500, twin barrels, 60 hours of reserve, 25,200 vph, Co-Axial escapement, silicon balance spring marked Si14.
- Dial: black with vertical teak lines, applied metal logo, framed date at 3 o'clock.
- Crystal and back: domed sapphire with anti-reflective coating, sapphire display back with the engraved Seahorse medallion.
- Water resistance: 150 m, so the case back and crown gaskets matter.
Where copies of this reference land
Three broad tiers show up in the market, and the price gap between them is wider than the visual gap.
Entry builds are a 41 mm case around a basic 28-series automatic with a decorated rotor. The dial print looks flat, the teak lines are shallow, thickness runs past 14 mm, and the date font is wrong.
Mid tier fixes the dial and the case profile and keeps the same movement underneath. Top tier is where the money goes: tighter case machining, better AR coating, bracelet end links that sit flush against the lugs, and a movement plate shaped to mimic the 8500 layout. Even there, the twin barrel bridge and the Si14 marking are cosmetic rather than functional.
Tells that survive a bad photo
- Thickness. Measure it. 13.2 mm is a hard number and thick builds show up fast with calipers.
- Dial texture. Tilt the watch under a lamp. Genuine teak lines catch light and shift; printed ones stay dull.
- Date window. The aperture should be crisp with an even bevel and a font that matches the rest of the dial.
- Bracelet fit. Run a thumb along the end links. A gap or a step against the case is the quickest give-away.
- Crown action. It should thread without catching and seat with no wobble.
- Case back. The Seahorse relief on copies is shallow and soft at the edges.
- Rotor noise and winding feel. A 28-series base feels and sounds different from a twin-barrel 8500.
Fit and wear notes
41.5 mm sounds large and wears smaller than the number suggests, because the lugs curve down and the bezel is thin. It suits wrists from roughly 6.5 to 7.5 inches. The 20 mm lug width means any 20 mm strap fits, which is worth remembering if you plan to move the bracelet onto leather or rubber.
What to ask before money changes hands
- Thickness measured with calipers, not copied from a listing.
- Which movement, plus a clear photo of the rotor and balance.
- Water resistance claim. Treat anything above 50 m on a copy as unverified unless it has been pressure tested.
- Return window, and whether the bracelet can be sized without stripped screws.
Bottom line
The honest version: a copy of the 321.10.42.50.01.001 can look convincing across a table and will never be the same object as the original. If you want the 8500, the twin barrels and the service network, only the real reference delivers them. If you are buying a copy with your eyes open, buy on the details above and never pay genuine money for it. Passing a copy off as the real thing is fraud, and that risk sits with the seller.