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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsThe Seiko Prospex Black Series 2021 pairs two automatic dive watches with the same dark, orange-accented night-diving theme: the angular SRPH11K1 Samurai and the more aggressively shaped SRPH13K1 Monster. Their key practical difference is straightforward: the Samurai has a 4R35 movement and date display, while the Monster has a 4R36 and day-date. Both offer about 41 hours of power reserve, silicone straps and 200 m diver’s water resistance. This is a specification-led comparison, not a claim of personal wrist time or dive testing.
What are the SRPH11K1 and SRPH13K1?
They are the automatic Samurai and Monster models in Seiko’s 2021 Prospex Black Series, a collection Seiko describes as inspired by the sea at dusk and at night. The manufacturer’s presentation centers on black finishes, orange details and LumiBrite intended to aid visibility in low light. The collection also included the solar SNE577P1; this comparison concerns only the two automatic references. Seiko’s Black Series 2021 collection page
Seiko India identifies SRPH11K1 as the Samurai and SRPH13K1 as the Monster, and lists their limited-edition quantities as 8,000 and 7,000 respectively. Those are stated production quantities, not evidence of how many remain available or what either watch is worth today. Seiko India’s Black Series page
SRPH11K1 vs SRPH13K1 specifications
| Specification | SRPH11K1 Samurai | SRPH13K1 Monster |
|---|---|---|
| Movement | Seiko 4R35, automatic with manual winding | Seiko 4R36, automatic with manual winding |
| Calendar | Date | Day and date, as reported at launch by Monochrome Watches |
| Power reserve | Approximately 41 hours | Approximately 41 hours |
| Case and strap | Hard-coated stainless-steel case; silicone strap | Black-coated stainless-steel case, as described in 2021 launch coverage; silicone strap |
| Crystal | Hardlex | Hardlex, as reported at launch by Monochrome Watches |
| Water resistance | 200 m / 660 ft diver’s | 200 m diver’s |
| Stated limited-edition quantity | 8,000 pieces (Seiko India) | 7,000 pieces (Seiko India) |
| Lug spacing | 22 mm (Seiko Philippines official store) | Not stated in the official store record reviewed |
Movement and core specification details are listed on Seiko Philippines’ SRPH11K1 product page and SRPH13K1 product page; the edition quantities appear on Seiko India’s collection page. The day-date and Monster crystal details are also given in Monochrome Watches’ July 23, 2021 launch report.
#1 Best Overall
How their shapes and displays differ
SRPH11K1 Samurai: angular case, simpler calendar
The Samurai’s defining visual cue is its angular case silhouette. Its 4R35 display supplies the date, without a day indication. Seiko Philippines lists 43 mm diameter and 48.1 mm lug-to-lug for this reference. Monochrome’s 2021 report gives different measurements—43.8 mm diameter, 13.4 mm height and 48.4 mm lug-to-lug—so the figures should not be blended into a single supposedly definitive set.
SRPH13K1 Monster: more assertive case, day-date
The Monster has the more aggressively shaped case and the 4R36’s day-and-date display. Monochrome’s 2021 report gives it dimensions of 42.4 mm diameter, 13.4 mm height and 49.4 mm lug-to-lug. Seiko Philippines’ page labels 42.4 mm as “Thickness” and 49 mm as “Diameter,” an apparent labeling error; those official-page figures are not reliable dimensions to repeat as stated.
Rank #2
- WATER-RESISTANT: these water-resistant men's dive watches are ISO scuba-approved to depths of 200 meters
- AUTOMATIC: these self-winding, automatic men's watches are powered by your movement, with a power reserve of 41 hours
- LUMIBRITE DISPLAY: this men's dive watch features a highly-legible display with LumiBrite hands and markers
- STAINLESS STEEL: features a durable stainless steel watch case and bracelet, unique case shape resembling teeth, and PADI red and blue colors on its elapsed timing bezel
- 4R36 CALIBER: equipped with the reliable caliber 4R36 automatic movement, this accurate men's watch keeps precise time
These published measurements suggest different proportions, but they cannot settle which watch will feel larger on a particular wrist. Case shape, lug reach and strap drape all affect perceived fit; trying the exact reference on is more informative than comparing diameter alone.
What the Black Series design means in use
Both watches share black cases and silicone straps, orange detailing, luminous displays and 200 m diver’s water resistance. Seiko frames LumiBrite and the dark treatment around night-diving legibility and the changing sea at dusk. That is the manufacturer’s design intent, not an independent low-light visibility or dive-test result. Their matching concept makes the decision less about choosing a different function category and more about preferring the Samurai’s angular profile or the Monster’s bolder one.
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Rank #3
- WATER-RESISTANT: these water-resistant men's dive watches are ISO scuba-approved to depths of 200 meters
- AUTOMATIC: these self-winding, automatic men's watches are powered by your movement, with a power reserve of 41 hours
- STAINLESS STEEL: features a durable 43.8mm stainless steel watch case and bracelet.
- LUMIBRITE DISPLAY: this men's automatic watch features a highly-legible display with LumiBrite hands and markers
- 4R35 CALIBER: equipped with the reliable caliber 4R35 automatic movement, this accurate men's watch keeps precise time
Fit, strap changes and daily ownership
The official Philippines store gives the Samurai 22 mm lug spacing, a useful starting point when checking replacement straps for that reference. The reviewed official Monster page does not state its lug spacing. Do not assume a strap width for the SRPH13K1 based on appearance or on the Samurai’s measurement; confirm fit against the specific watch before ordering. Both are supplied with silicone straps.
The approximately 41-hour reserve is the stated figure for each movement. If either watch is left unworn longer than that, it may stop and need winding and resetting before use. The 4R35’s date and the 4R36’s day-date are the calendar distinction to weigh if you want fewer displayed indications or prefer seeing the weekday as well.
Rank #4
- AUTOMATIC MOVEMENT: Seiko 4R35 automatic movement includes manual winding, 23 jewels, date display, stop-second function, and approximately 41 hours of power reserve.
- 200M DIVER'S WATER RESISTANCE: Rated to 200 meters / 660 feet for diving, with a screw-down crown and screw case back.
- STAINLESS-STEEL CASE: 41.7mm stainless-steel case measures 12.3mm thick with a 49.5mm lug-to-lug distance and 20mm lug width.
- HARDLEX CRYSTAL: Durable Hardlex crystal protects the dial, while LumiBrite on the hands, indexes, and bezel improves low-light visibility.
- DIVER-READY DESIGN: Unidirectional rotating bezel and three-fold clasp with secure lock, push-button release, and extender provide practical functionality.
Limited editions and launch pricing
Seiko India lists 8,000 Samurai examples and 7,000 Monster examples. The 1,000-piece difference establishes the stated edition sizes only; it does not establish current scarcity, resale performance or investment potential.
Monochrome Watches reported 2021 launch prices of EUR 490 for the SRPH11K1 and EUR 480 for the SRPH13K1. These are historical launch figures, not current prices, and should not be treated as a present-day quote for another region or retailer.
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- SEIKO WATCH – Seiko SRPL15 Prospex wristwatch.
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- MODEL REFERENCE – SRPL15 identifies the specific model.
- WATCH DIAMETER – 41.7 mm.
Availability: check by region and seller
When the Seiko Philippines official-store pages were checked in 2026, both references were displayed as sold out. That is a regional stock snapshot; it does not establish global discontinuation or the status of authorized retailers elsewhere. Seiko India’s page also lists regional rupee prices, which are not universal pricing. For a current purchase, check an authorized Seiko retailer in your country and verify the full reference number. Marketplace listings can use similar names or images, so confirm that a listing identifies SRPH11K1 or SRPH13K1 and the 2021 Black Series edition before relying on it.
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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
