The Beginner’s Guide to Watch Case Back Markings

Types of Case Backs

Before examining the markings, it helps to understand the three main case back styles, because the type of back often determines which markings are present and where they appear.

• Snap-on back: Pressed into place against a rubber gasket. Common on dress watches and affordable quartz models. Markings are engraved or stamped on the outer surface. A watchmaker pries it off with a case knife.
• Screw-down back: Threaded into the case body, creating a compression seal. Standard on sport and dive watches. The outer surface typically features fluted notches around the perimeter for a case-back wrench. Markings appear on the flat center area.
• Exhibition (display) back: A transparent sapphire or mineral glass window that lets you view the movement. Markings are usually engraved on the surrounding metal ring rather than on the glass. Common on higher-end mechanical watches.

Serial Numbers vs. Model Numbers vs. Caliber Numbers

Three different numbers often appear on or inside the case back, and beginners frequently confuse them:

• Serial number: A unique identifier for that specific watch. No two watches of the same brand should share the same serial. It is used for authentication, warranty tracking, and production dating. Typically 6–10 digits.
• Model / reference number: Identifies the specific model configuration — case size, dial color, bezel type, bracelet. All watches of the same configuration share the same model number. Example: Rolex “126610LN” is the 41mm black-dial Submariner with date.
• Caliber number: Identifies the movement inside the watch. Sometimes engraved on the case back, sometimes only visible on the movement itself. Example: Omega “Cal. 3861” is the manual-wind Moonwatch movement.

Water Resistance Ratings Explained

The water resistance rating is one of the most misunderstood markings on a watch. Here is what the numbers actually mean in practical terms:

• 3 BAR / 30m / 3 ATM: Splash-proof only. Safe for hand washing and light rain. Do not swim or shower with this watch.
• 5 BAR / 50m / 5 ATM: Suitable for brief, shallow swimming. Not suitable for diving or high-impact water sports.
• 10 BAR / 100m / 10 ATM: Suitable for recreational swimming and snorkeling. Not for scuba diving.
• 20 BAR / 200m / 20 ATM: Suitable for recreational scuba diving (with a dive bezel). The ISO 6425 standard for dive watches.
• 30+ BAR / 300m+: Professional diving depth. Watches rated to 300m or more typically feature helium escape valves for saturation diving.

Important: these ratings are based on static pressure tests. The dynamic pressure of a moving arm hitting water (as in swimming strokes) or a shower jet can exceed the rated pressure. Also, water resistance degrades over time as gaskets age. Have your watch pressure-tested every 1–2 years if you regularly expose it to water. For a deeper dive into this topic, see our water resistance markings guide.

Material Stamps

Case back material markings tell you what the watch is made of. Common stamps include:

• Stainless Steel / St. Steel / SS: The case is stainless steel, typically 316L or (for Rolex) 904L alloy.
• Stainless Steel Back: Only the back plate is steel; the rest of the case may be base metal, brass, or alloy.
• Titanium / Ti: Lightweight, hypoallergenic, and corrosion-resistant. Common on Citizen Promaster and Seiko Astron models.
• 18K / 750: 18 karat gold (75% gold content). Typical for luxury watches from Rolex, Patek Philippe, and Audemars Piguet.
• Gold Plated / GP / Gold Electroplated: A thin layer of gold over a base metal core. Not solid gold.
• Base Metal / All Metal / Alloy: The case is made from non-precious metal alloy, common on fashion watches.

Swiss Made and Japan Made Labels

The “Swiss Made” designation is legally protected under Swiss law. To carry this label, a watch must meet specific criteria: the movement must be Swiss, the movement must be cased in Switzerland, and at least 60% of the manufacturing costs must be incurred in Switzerland. Variations include “Swiss” (movement only is Swiss), “Swiss Parts” (some components are Swiss-made), and “Swiss Mov’t” (the movement is Swiss but the watch may be assembled elsewhere).

“Japan Made” or “Made in Japan” indicates that the watch was assembled in Japan. “Japan Movt” or “Japan Movement” means only the movement was manufactured in Japan — the rest of the watch may have been made elsewhere. Japanese movements from Miyota and TMI are widely used in affordable watches worldwide.

Brand Logos and Emblems

Many manufacturers engrave or emboss their logo on the case back. These can be helpful for identification when the dial brand name is worn or missing:

• Omega seahorse (Hippocampus): Found on Seamaster models from the 1950s onward. The specific seahorse design helps date the watch.
• Rolex coronet: Modern Oyster-case Rolex watches do not have a logo on the case back. If you see one, investigate further.
• Tudor rose / shield: Tudor’s case back logo has evolved from a rose to a shield over the decades.
• Seiko tsunami / wave: Indicates the Prospex or Marinemaster diver line.
• Longines winged hourglass: One of the oldest registered trademarks in watchmaking, applied to case backs since the 19th century.

What NOT to Worry About

Some marks on a case back are not significant and should not cause concern:

• QC stickers: Small adhesive labels or holographic stickers left from factory quality control. Removing or leaving them is a personal choice — they do not affect value on most watches (Rolex green stickers are an exception for some collectors).
• Casio module numbers: Casio prints a four-digit module number (e.g., “3459”) on the case back for manual reference. This is normal and not a defect.
• Factory tool marks: Minor scuff marks around the case back perimeter from the tool used to open or close the case. These are nearly unavoidable during servicing.
• Engraved inscriptions: Personal dedications, retirement gifts, or military issue markings. These may add historical interest but do not indicate a problem with the watch itself.