Seiko · Prospex Divers

Strap for Prospex Diver 1970 Stainless Steel / Grey - Brown / NATO

Takes 20 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width20 mm
Case diameter43 mm
ReferenceSPB237
FamilyProspex Divers
MovementSeiko caliber 6R35 hours, minutes, seconds | date
Year2021
CaseStainless Steel

Spring bar

Swiss Standard universal spring bars

The right category for this model · 316L steel, all lug widths 13–26 mm

Straps for the Prospex Divers SPB237

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The Prospex Divers SPB237, seen from the bench

The Seiko Prospex Divers SPB237 is a 42.70 mm stainless steel diver watch with a 20 mm lug width, powered by the automatic caliber 6R35. Built on the Prospex line founded in 1965 for underwater instruments, it features a unidirectional bezel, Hardlex crystal, and 300-meter water resistance. The movement offers four days of power reserve at 21,600 beats per hour.

Frequently asked questions

What is the lug width of the Seiko Prospex Divers SPB237?

The lug width of the SPB237 is 20 mm. This measurement represents the internal distance between the two lugs of the case and determines compatibility with aftermarket straps. Verification is essential before purchase: position a digital calliper between the lugs, measuring from inside to inside, excluding any decorative protrusions.

What is the best strap for the SPB237?

Selection depends on use and wrist preferences. For formal elegance, we recommend a vegetable-tanned calf leather in dark brown on a stainless steel deployante, which dialogues with the case's substantial mass. To emphasise diving functionality, a NATO in grey or military-green canvas is ideal. For wet environments, matte rubber remains the most practical choice, guaranteeing grip and rapid drying.

How do you change the strap on the Seiko Prospex Divers SPB237?

The SPB237 uses spring bars that fasten the strap to the case lugs. With a spring bar tool, press inward on one side of the bar until it yields, removing it gently. Align the new strap hole with the bar and press in until it clicks. Repeat on the opposite side. Straightforward but requires precision to avoid scratching the case.

Is a 20 mm aftermarket strap compatible with the SPB237?

Yes, any strap with certified 20 mm lug width is mechanically compatible with the SPB237. Compatibility is guaranteed if the internal width of the strap (between the two spring bar holes) matches exactly 20 mm. Always verify strap thickness as well: if excessive, it may not slide correctly through the lugs.

How long does a leather strap last on the Seiko Prospex Divers SPB237?

Longevity depends on leather quality, usage conditions and humidity exposure. Superior vegetable-tanned calf leather, worn primarily in dry environments and subjected to regular maintenance, can last 5-7 years. Frequent exposure to saltwater, intense perspiration or direct sunlight significantly reduces lifespan. To extend durability, we recommend periodic application of protective balms and immediate drying after water contact.

The next step

The right strap isn't chosen. It is built, together.

From the atelier appointment to delivery, every step is made for those who know that things done well take time. Rare leathers, one piece at a time, eighteen months of warranty.

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Casati Milano · Via XX Settembre 15, Milan · by appointment only