Model Number Stamp — What This Mark Means

The model number tells you exactly which product line and variant your watch belongs to. It often encodes the movement, case, and sometimes the dial or bracelet configuration, making it the key identifier when searching for specifications, compatible parts, or current market value.

Japanese brands tend to make this encoding explicit. Seiko's caliber-case format places the movement before the hyphen and the case design after it: 7S26-0020, for example, identifies the 7S26 automatic movement in the case used by the SKX007 diver. Citizen uses codes such as BN0150-28E, where the suffix typically distinguishes color variants.

Casio splits the job in two: the model number (such as F-91W) identifies the watch, while a separate module number identifies the electronics inside. Swiss brands more often use the term reference number for the same idea.

The model number is typically stamped or engraved on the case back, near the center or around the perimeter, alongside the serial number and water resistance marking. On Seiko and Citizen watches it is usually the most prominent alphanumeric code on the back.

On Casio watches, look for the model on the case back and the module number inside a small stamped rectangle. Many Swiss watches engrave the reference between the lugs instead, hidden until the strap is removed.

Each brand has its own format. Seiko uses the caliber-case pattern (7S26-0020, 6R15-00A0), Citizen uses alphanumeric codes like BN0150-28E, Tissot uses long T-prefixed references, and Casio combines short model names with four-digit module numbers. Some brands add regional suffixes for different markets.

Presentation varies by era as well. Vintage case backs were typically stamped with deeper, sometimes uneven characters, while modern backs are often laser-etched with fine, uniform text. A few brands list the full model code only inside the case back or on the papers.

People often confuse the model number with the serial or caliber number. The model number identifies the product line and is shared by every example; the serial is unique to yours; the caliber names the movement, though in Seiko's format it forms the first half of the model code.

The same model number also does not guarantee identical specifications across all production years, since dials, lume, and even movements can change quietly within a long-running reference.

Search the model number online to find your watch's full specifications, user manual, and compatible accessories. For Casio watches, search the module number to retrieve the correct manual; for Seiko, the caliber-case code leads to parts lists and crystal and gasket references.

Keep the number on hand when contacting customer service or ordering parts such as straps, crystals, or bezels; it is usually the first thing a service center asks for.