What 321.10.42.50.01.001 Actually Is

Reference 321.10.42.50.01.001 identifies an Omega Seamaster Aqua Terra 150M Master Co-Axial. The number resolves to a stainless steel case measuring 41.5 mm, a black dial, and a steel bracelet on a folding clasp. Omega built it around the Master Co-Axial calibre 8500, a twin-barrel automatic movement with a silicon balance spring and a resistance to magnetic fields of 15,000 gauss or more. Water resistance is rated to 150 meters, and the caseback is sapphire, so the movement is visible from the back.

The reference number is the part that matters. Omega assigns one to every case, dial, bracelet, and movement combination it ships, and service centers use it to pull the correct parts. A counterfeit does not carry a real version of this number, because the number belongs to a genuine configuration that only Omega produces. Anyone selling a watch described as this reference is either selling an authentic Omega or misrepresenting what they have.

Specifications at a Glance

  • Case: stainless steel, 41.5 mm diameter
  • Dial: black with a horizontal teak pattern and a date window at 3 o'clock
  • Movement: Omega calibre 8500, automatic, Master Co-Axial escapement
  • Crystal: domed sapphire with anti-reflective coating on both faces
  • Water resistance: 150 meters
  • Bracelet: steel with a push-button folding clasp

How to Verify a Genuine Example

  1. Read the reference number engraved on the caseback and compare it digit by digit against 321.10.42.50.01.001.
  2. Check that the eight-digit serial number on the caseback matches the one printed on the warranty card and the Master Chronometer certificate.
  3. Inspect the dial text under magnification, since genuine printing sits sharp against the surface with no bleeding at the edges of the letters.
  4. Look at the teak pattern on the dial, which should run in even horizontal lines with no misalignment at the date window.
  5. Confirm the date changes cleanly at midnight rather than drifting over several hours.
  6. Examine the bracelet end links, which should sit flush against the case with no gaps and no wobble.
  7. Ask a qualified watchmaker to open the caseback and confirm the calibre 8500 rotor, bridges, and finishing.

Buying One Without Getting Burned

  1. Ask the seller for the reference number, the serial number, and the year of production in writing before you discuss price.
  2. Request close-up photos of the caseback engraving, the clasp, and the movement through the sapphire back.
  3. Meet at an authorized Omega service center or an independent watchmaker for a paid inspection.
  4. Verify the serial number with Omega or an authorized dealer before money changes hands.
  5. Pay with a method that gives you a documented dispute process, and keep the receipt.

Why This Page Does Not Point to a Replica

A replica Aqua Terra cannot be checked against this reference, because the reference describes tolerances, materials, and a movement that a copy shop does not have. Replica pieces use generic movements, plated cases, and printed dials that fail every step in the list above. If the goal is a 41.5 mm steel sports watch on a bracelet with a black dial, there are honest options at several price points from established brands. If the goal is this exact watch, buy it used from a seller who will let a watchmaker open it first.