Seiko’s 38.0 mm SKX-series lineup includes three documented models: the SRPK29, SRPK31 and SRPK33. Their listed dimensions are 38.0 mm across, 44.2 mm lug-to-lug and 12.1 mm thick, giving a more useful starting point for assessing fit than case diameter alone. Each cited specification page lists Seiko’s 4R36 automatic movement, day-date display and 10 bar water resistance.
Which Seiko 5 Sports models have a 38 mm case?
Seiko’s U.S. SKX-series page lists the SRPK29, SRPK31 and SRPK33. The brand describes the collection as “Inspired by the Seiko SKX series, one of Seiko’s best-loved sports watches”; that is Seiko’s own heritage framing. See Seiko’s SKX-series lineup.
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SRPK29
The SRPK29 appears on Seiko’s U.K. product page. Check the exact regional listing and its images to confirm the dial and bezel appearance before buying. View the U.K. SRPK29 specification page.
SRPK31
The SRPK31 appears on Seiko’s U.S. product page. The page displayed a manufacturer-listed price of USD 350 when reviewed on October 8, 2026; it is a regional list price, not a universal price or a live third-party offer. View the U.S. SRPK31 specification page.
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- Case Diameter: 42.5mm
- Case Thickness: 13.9mm
- Case Length: 46 Mm
- Lug Width: 22mm
SRPK33
The SRPK33 appears on Seiko’s India product page. Confirm the exact reference and regional terms on the listing for your market. View the India SRPK33 specification page.
How big is the SRPK31, and what do the dimensions mean?
Seiko lists the SRPK31—and the cited SRPK29 and SRPK33 pages—with a 38.0 mm case diameter, 44.2 mm lug-to-lug length and 12.1 mm thickness. The specifications were reviewed on October 8, 2026. Lug-to-lug length indicates how far the watch spans across the wrist, while thickness affects how much it rises above the wrist. Wrist shape and personal preference matter, so these measurements help narrow expectations but cannot determine fit for everyone.
What movement and functions do the three models share?
The cited Seiko specification pages list the 4R36 automatic movement with manual winding, approximately 41 hours of power reserve, 24 jewels and stop-seconds. They also list a day-and-date display. These are manufacturer-listed specifications, not independent measurements of timekeeping accuracy or reserve in use.
- Movement: Seiko 4R36 automatic, with manual winding.
- Power reserve: approximately 41 hours, as specified by Seiko.
- Jewels and setting: 24 jewels and stop-seconds, as specified by Seiko.
- Calendar: day and date display.
What are the construction and water-resistance specifications?
Seiko lists a stainless-steel case, Hardlex crystal, LumiBrite on the hands and indices, a unidirectional rotating bezel, and a screw-down, see-through case back. The pages also list 10 bar water resistance and 4,800 A/m magnetic resistance. A rating is not a guarantee of real-world performance or suitability for every underwater activity; these official specifications do not independently establish water performance, durability or long-term reliability.
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- Includes individual box, instruction manual (English language not guaranteed)
- Mechanical automatic movement (with hand winding)
- Day difference + 45 to -35 seconds
- Lasts approximately 41 hours on maximum winding
- Calendar (Date/Day) function included
What strap size fits the SRPK31?
Seiko lists a 20 mm distance between the lugs on the cited models. That measurement is a useful starting point when searching for a replacement strap, but a 20 mm width alone does not establish that every strap or bracelet will fit the case or its attachment hardware. Check the strap’s attachment style and hardware requirements against the actual watch and product listing.
How should you choose between the SRPK29, SRPK31 and SRPK33?
The cited pages establish shared core specifications, but do not provide a complete verified colorway-by-colorway comparison. Treat the reference number and exact regional listing as essential when comparing appearance and purchase terms.
- Appearance: compare dial and bezel images on the exact model listing; do not assume a reference’s appearance from another region’s page.
- Fit: consider all three measurements—38.0 mm diameter, 44.2 mm lug-to-lug and 12.1 mm thickness—along with your wrist shape and preferred proportions.
- Band: use the stated 20 mm lug spacing as a starting point, then verify attachment and hardware compatibility.
- Purchase terms: compare current local pricing, seller identity, warranty, condition, shipping and return policy. The SRPK31’s U.S. displayed price and SRPK29’s U.K. displayed price are regional manufacturer listings, not directly comparable universal prices.
Seiko’s U.K. SRPK29 page displayed GBP 310 when reviewed on October 8, 2026. Check the live regional page and retailer terms for current availability and price.
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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.
