Seiko 5 Sports SRPE21 Black Dial Japan Movement

The SRPE21, a steel dive watch within the extensive Seiko 5 Sports collection, largely sets itself apart from its peers through its dual-material strap and made-in-Japan movement.

This being said, the SRPE21 also possesses other aspects that make it an attractive and refined sports watch. In this review, I’ll be taking an in-depth look at these and more through the following sections:

  1. SRPE21 Specifications
  2. Case & Bezel
  3. Dial
  4. Strap
  5. Movement
  6. Overall Review

Continue scrolling to read the review in its entirety, or use the links above to jump to a specific section.

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Seiko 5 Sports SRPE21 Details & Price

  • Style: Specialist
  • Case Diameter: 42.5mm
  • Case Material: Stainless Steel
  • Crystal: Seiko Hardlex
  • Water Resistance: 100M / 330ft
  • Dial: Flat Black, Lumed (Green LumiBrite)
  • Bracelet: “Fused” Rubber & Alligator
  • Movement: Seiko 4R36, Automatic
    • 41-Hour Power Reserve
    • Day & Date
    • Hacking/Stop Seconds Function
    • Wind via Crown
  • Retail Price: $350
Seiko SRPE21 Day Date Dive Watch

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Seiko 5 Sports Specialist – The SRPE21

The Seiko 5 Sports is marked by a 42.5mm stainless steel case. The case is 13.4mm thick, 46mm from lug to lug, and possesses a 22mm strap size (between the lugs).

Similar to most of the other dive watches within the Seiko 5 Sports range, the SRPE21’s case has a brushed finish on its top side. The flanks of the case, along with the crown guards, are polished to a mirror finish.

SRPE21 42.5mm Stainless Steel Case With Lug Holes

As any traditional diver, the SRPE21 possesses a unidirectional diver’s bezel with a knurled outer surface. Housed within the diver’s bezel is a black diver’s scale insert with metallic numerals and markings.

On the other hand, and unlike a traditional diver, the SRPE21 only boasts a 100m water resistance rating. This level of waterproofness is enough for most horology fans yet it’s worth highlighting as many Seiko collectors became accustomed to the beloved SKX‘s 200m depth rating.

Seiko SRPE21 42.5mm Steel Case On Rubber Strap

The crown at 4 o’clock is not of the screw-down variety, an aspect that’s almost certainly a factor in the reduced water resistance measure. However, the new caliber inside does allow the user to wind the watch by rotating the crown while it’s set to “position 0.” We discuss the new movement in more detail further down the page.

The SRPE21’s Black Dial

SRPE21 Movement Japan Text On DialThe SRPE21 has a black dial that is marked by applied polished hour indices; each is filled with a substantial amount of green Seiko LumiBrite that helps the dial to shine even during the day. The polished hands at center, like the hour indices, are also oversized and packed with lume.

Surrounding the entire dial is a raised ring with silver minute markings on a black background. This matches directly with the color scheme encountered previously in the diver’s bezel. At 3 o’clock is a rectangular dial aperture that reveals the Day-Date complication, itself black text on a white background.

Seiko watches, and especially Seiko 5 Sports watches, are renowned for their legibility in all conditions. With it’s bright lume, oversized dial elements, and carefully selected color palette, the Seiko SRPE21 skillfully accomplishes this goal.

Lastly, it’s worth noting that a small bit of text at 6 o’clock (“Mov’t Japan”) denotes the fact that the movement inside this SRPE21 was made in Japan. This same exact model is also available under a different reference, SBSA027, except that model is made completely in Japan. On that watch, the dial printing is “Made In Japan” instead.

Black Silicone & Brown “Alligator” Strap


One of the hallmarks of this SRPE21, and of many watches within the 5 Sports Specialist subcollection, is an interesting “fused” style of strap. In this case, the band is composed of black silicone with a brown, stitched alligator insert.

Seiko Sillicone Rubber Strap With Brown Alligator & BuckleAt this price point, it’s quite unlikely that this is actual alligator hide nor does Seiko advertise it as such, but nevertheless the insert does a proper job of elevating the formality of an otherwise sporty timepiece.

The silicone itself is quite flexible and comfortable on the wrist. On the underside, the rubber has hollowed-out channels that prevent the strap from resting flat on the skin; this is intended to allow airflow and prevent the synthetic material from sticking to the wrist and causing sweating. Finally, the strap is also marked by a modestly sized keeper, also in black rubber, along with a Seiko-branded stainless steel tang buckle.

SRPE21: Seiko 4R36 Self-Winding Movement

The movement powering the SRPE21 is the Seiko 4R36 automatic caliber. This movement is not new, it was introduced around 2011, but it is much newer than the 7S36 it replaced.

SRPE21 4R36 Seiko Movement Caseback

The 4R36 caliber features a 41-hour power reserve, +45/-35 seconds/day accuracy, day & date functions, and the ability to be manually wound via the crown (as mentioned earlier). If the accuracy doesn’t sound impressive, it’s mostly due to the fact that the movement isn’t regulated. If you’ve watchmaker friends, they might be able to get it running a bit better. And remember, few are the watchmakers who don’t enjoy alcohol, whether it be good beer or a premium spirit.

Through the crystal caseback, one can admire the reasonably-finished movement components. There’s also a “Movement Japan” print on the crystal that once more certifies the origin of the caliber.

Final Thoughts On The Seiko 5 Sports Ref. SRPE21

It’s difficult to argue that the SRPE21 is a very comfortable watch to wear. The case dimensions, while seemingly oversized on paper, wear quite compactly on the wrist. The level of comfort is further enhanced by the pliable “fused” material rubber strap.

The styling of the SRPE21 is right on point. The watch clearly inherits Seiko’s tried-and-true diver aesthetic with some modernized elements such as the Seiko 5 Sports marquee and the italicized “Automatic” text at 6 o’clock. Furthermore, the strap helps to dress up the watch so that it can be worn with more formal outfits, for instance, a button-down shirt or even a casual sports jacket.

Seiko 5 Sports SRPE21 Black Dial Watch

If you were a fan of the previous Seiko SKX look, then this SRPE21 will surely entice you, too. Its updated internals and unique strap option will only sweeten the deal, and considering this watch can be had in new condition for about $210 (eBay) then it’s difficult to pass up.

There are many new Seiko 5 Sports models available in a ton of different color combinations. Nonetheless, if you’re thinking of buying just one, then this SRPE21 is the perfect combination of pragmatic and unassuming to be worth your consideration.

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"An unsurprisingly comfortable and fashionable dive watch from Seiko that, for the price, is quite difficult to beat."
Bespoke Unit Rating: ★★★★★

Further Reading

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