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seiko case shapes

Seiko Case Shapes

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The Seiko dynasty began in 1881 with a small shop in central Tokyo repairing and selling timepieces. In the more than 140 years since then, the designers and engineers at Seiko have become justly celebrated for their technical innovation. That extends to every aspect of watch design, but one area that deserves special recognition is in Seiko’s unique case shapes (and their nicknames!). Read on to learn more about them.

seiko prospex snj025

The Tuna

Seiko Prospex SNJ025

The watches of the Seiko Tuna Collection are known for the distinctive tuna can-like shape of their cases with screw-down crowns, screw-in casebacks and unidirectional rotating bezels. The Prospex SNJ025 is a modern interpretation of the 1982 Hybrid Diver’s Watch with water resistance to 200 meters. This solar diver is powered by light energy—no battery change required—with a six month power reserve once fully charged. The stainless steel and plastic case is matched with a black silicone strap. The black dial features an alarm, LED light and Lumibrite hands and hour markers for maximum readability. The watch featured above actually has two nicknames! While it features Seiko’s “Tuna” case, the SNJ025 is known as the “Arnie” thanks to its appearance on Arnold Schwarzenegger’s wrist in the film Predator.

seiko prospex spb147

The 62mas

Seiko Prospex SPB147—1965 Diver’s Modern Re-interpretation

One of the most heralded cases in Seiko’s long history, the original 62MAS was Seiko’s first professional diver’s watch. The name “62MAS” was derived from the first two digits of the reference number and autoMAtic Selfdater. Standard issue today, the quick-set date was an important innovation of the time. This modern re-interpretation of the 1965 original has a stainless steel case with super hard coating, screw-down crown, screw-in caseback and anti-reflective curved sapphire glass crystal. The sumptuous brown dial features a date indicator and Lumibrite hands and hour markers. The black silicone strap is ideal for divers.

prospex seiko ocean conservation turtle diver srph57

The Turtle

Seiko Prospex Ocean Conservation Turtle Diver SRPH57

With their rounded corners and soft curves, the Seiko watches featuring the “turtle” case shape, when viewed from above, remind many people of a turtle shell. They are absolutely diver’s watches, but also are designed for all-day wear with comfort in mind. This Ocean Conservation Turtle Diver has a stainless steel case, a unidirectional rotating bezel with ceramic insert and an anti-reflective sapphire crystal. The dazzling dial in gradient turquoise features a sea turtle shell motif and includes a day and date indicator and Lumibrite hands and hour markers. Seiko’s “roundest” case, the Turtle is unique in its use of straight endlinks. Notice the region where the bracelet meets the case – it’s not curved! This is rare in watchmaking and makes the Turtle even more special.

prospex seiko srpb99

The Samurai

Seiko Prospex SRPB99 Samurai

When Seiko introduced the first Samurai model in 2004—so named because the minute hand was shaped like a sword—it was immediately considered one of their most accomplished diver’s watches. The nickname is even more perfect thanks to the sharp edges of the stylized case. The Prospex SRPB99 is a worthy addition to the collection, with water resistance to 200 meters. The stainless steel case features a unidirectional rotating bezel in red and blue. The black dial is accented with a textured wave pattern, and includes date indicator, Lumibrite hands and hour markers. The stainless steel bracelet is the perfect accompaniment.

prospex seiko spb191 diver shogun

The Shogun

Seiko Prospex SPB191 Diver Shogun

In 2008, Seiko was proud to launch a new family of diver’s watches. Named for their armor-like appearance, shogun watches are amazingly durable, yet have a surprising lightness thanks to their titanium construction. The case of the Prospex SPB191 has a super hard coating, along with a screwed case back, screw-down crown and unidirectional rotating bezel. The black silicone strap offsets a white dial with a date indicator and Lumibrite hands and hour markers.

Discover the full line of celebrated Seiko watches at Feldmar. Browse our online store or stop into our flagship location.

About The Author: Tom Roth


Born in Washington state, Tom developed an interest in photography during college at University of San Diego. There, he got started in music journalism, interviewing artists and taking photos at concerts. A life-long tinkerer and collector, it wasn’t long before Tom became fascinated with fountain pens and watches.

Those interests collided in November 2020 when Tom started at Feldmar Watch Company where he lives out every watch geek’s dream: photographing and writing about timepieces. When he’s not tinkering with his watch collection, Tom can be found traveling, biting his nails while watching PNW sports teams, and taking flying lessons.

Read more from Tom Roth

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