The core advice: judge a replica Omega 3604 by four measurable things, not by branding words. Those four are case diameter and thickness, dial printing and lume tone, crystal material, and movement grade. Ask the seller for photos of the exact unit they will ship, with a ruler beside the case and a clear shot of the movement through the caseback. If you get catalog renders instead, walk away. Everything below is detail on how to check those four points.

One warning before the rest. A watch carrying a trademarked logo is a counterfeit, and counterfeit goods can be seized at import in the United States and most of the European Union. Spend only what you can afford to lose, and read the legal note near the end.

What the 3604 designation covers

Vintage Omega reference numbers were assigned by catalog block rather than to a single model, and the 3600 series falls in the mid-century period when Omega built small, thin dress and sports cases with hand-wound or bumper automatic movements. Replica listings use the number loosely, so two sellers offering a 3604 can be shipping different watches. Before you compare sellers, fix the genuine specification you are aiming at: case diameter, lug width, dial layout, hand shape, and movement family. Archive extracts from the manufacturer and published collector references are the fastest way to pin that down.

What to look for

• Case: diameter within one millimeter of the target, correct lug width, era-correct lug profile, and no soft or over-polished edges on a vintage finish.
• Dial: print weight and font, logo application, minute track alignment, and lume plots that match the hands in color and age.
• Hands: correct shape and length so they reach the right part of the minute track.
• Crystal: acrylic on a period build, with a domed profile rather than a flat generic disc.
• Crown: correct diameter and signature, with smooth winding and no grinding.
• Movement: the actual caliber, not a marketing name. Request a photo and a beat-rate reading.
• Caseback: engraving depth, stamping style for reference and serial, and gasket condition.
• Strap or bracelet: correct lug fit, end links that do not rattle, hardware that matches the case finish.

Parameter bands worth asking about

• Case diameter: 33 mm to 36 mm for mid-century references. Anything at 40 mm or above is a modern reinterpretation, not a period build.
• Lug width: 18 mm in most cases, sometimes 17 mm or 19 mm. Confirm it, because a wrong lug width means none of your straps fit.
• Case thickness: 9 mm to 11 mm. Thicker cases suggest an automatic movement squeezed into a dress profile.
• Weight, head only: 25 g to 45 g in steel. Very light cases feel hollow and often use plated brass.
• Gold plating: 3 to 5 microns for a build meant to be worn. Under 2 microns, plating wears through at the lugs within months.
• Beat rate: 21,600 or 28,800 vibrations per hour. A claimed high beat with a 21,600 reading means the seller is describing a movement they are not shipping.
• Power reserve: 36 to 42 hours on a serviced movement. Under 24 hours points to a worn or low-grade unit.
• Crystal: 1.0 mm to 1.5 mm acrylic, or 1.5 mm to 2.0 mm sapphire if you prefer scratch resistance over period look.

Movement tiers

Entry tier is a Chinese 21-jewel automatic from the 2813 family: cheap, noisy rotor, around 21,600 beats, and best treated as disposable. Mid tier is a Seagull or Hangzhou automatic, or a clone of the Swiss 2824 pattern: better finishing, 28,800 beats, and parts a watchmaker can replace. Upper tier is a genuine Swiss 2824, Sellita SW200, or a period-correct hand-wound Swiss caliber, which is where cost and reliability both jump. Decorated movements with engraved bridges but no verifiable marking sit in the entry tier no matter how the listing describes them.

Pitfalls that cost the most

• Stock photos instead of real images of the unit in stock. This is the most common problem in the category.
• Swiss labels on watches in the budget tier. A genuine Swiss movement pushes a build into a different class.
• Vague sizing. If the listing omits diameter and lug width, expect a mismatch.
• Plated cases sold as solid gold or solid steel.
• No written return window, or a policy that excludes shipping damage and water ingress.
• Ignoring how a 34 mm case wears. It reads small by modern standards, and that surprises buyers used to 40 mm.
• Assuming resale value. Counterfeits hold almost none, and forums and marketplaces pull listings that carry logos.
• Forgetting seizure risk. A low price is no bargain if the parcel is confiscated.

FAQ

Is the Omega 3604 a real reference?

Yes, the number sits in a genuine vintage Omega block, but the specification attached to it shifts by catalog year. Verify case size, dial layout and movement family against archive data or a collector reference before you buy, because sellers apply the number to several different builds.

Which movement should I pick for a daily wearer?

A clone of the Swiss 2824 pattern or a Seagull automatic at 28,800 beats. They keep time, tolerate a knock, and any watchmaker can service them. Choose a hand-wound Swiss caliber only if you want the period feel and accept higher service costs.

Can I wear it swimming?

Treat any replica as splash resistant at best. Gaskets are often dry or missing, and vintage case designs with press-fit backs were never built for modern depth ratings, whatever the caseback says.

What should I check the day it arrives?

Measure the case and lug width, time it against a reference clock for 24 hours, listen for rotor noise, check the crown for smooth winding, and photograph everything before you wear it. That record is what supports a return claim.

The legal side, in one paragraph

Counterfeit watches infringe trademark law. United States Customs and Border Protection can seize parcels and pursue civil penalties, and most sellers place import risk on the buyer in their terms. Nothing in this guide changes that, so count the cost of a lost shipment as part of the real price.