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Also uses Seiko Cal. 6R35

Seiko Prospex 1970 Willard Re-creation SPB153 Ref. SPB153J1, black dial, steel case
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Seiko Prospex Alpinist SPB121 Ref. SPB121J1, green dial, steel case
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Seiko Prospex Sumo SPB103 Ref. SPB103J1, blue dial, steel case
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Seiko Presage Sharp Edged SPB169 Ref. SPB169J1, blue dial, steel case
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Seiko Presage Sharp Edged Ref. SPB407J1, black dial, steel case
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Presage Sharp Edged
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Prospex
Medium-large: suits wrists 6.5 in+ (16.5 cm+)
40.5 mm case. Wears confidently on average to larger wrists. May overhang on slender builds.

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Authentication

Low counterfeit risk overall, but bezel inserts and bracelets are frequently swapped on used examples.

Known issues in the market
  • Bezel inserts replaced with aftermarket units that lack the correct matte finish and lume pip size.
  • Grey-market examples with bracelet end links that fit poorly, leaving visible gaps at the case.
  • Dial printing on fakes shows blurred "Professional Diver's 200m" and "Prospex" text under magnification.
  • Crown protector at 4 o'clock is a small tab; worn or missing protectors indicate heavy use or a replacement case.
AreaWhat to checkWhat is correctRed flag
caseMatte black aluminium insert with lume pip at 12Insert surface is uniformly matte black with no gloss; lume pip at 12 is white and rectangular; 120 click detents are positive and even; numbers and triangle markings are crispAny gloss finish on the insert; pip that is round instead of rectangular; soft or skipped detents; blurred minute markings
dial"Professional Diver's 200m" and "Prospex" textText is clean and evenly spaced under 5x loupe; "SEIKO" at 12 is bold and sharp; applied indices have clean lume fill with no overflowAny blurring of text under magnification; uneven character spacing; lume overflow or bubbles in applied markers
crownCrown protector at 4 o'clockSmall crown guard tab is present and symmetrical; crown screws down smoothly; no play when screwed inMissing crown guard; crown that wobbles or does not screw down completely; signs of grinding or filing around the crown tube
braceletEnd link fit at the caseEnd links sit flush against the case lugs with no visible gap; bracelet material matches the case finish (brushed sides, polished center)Visible gap between end links and case lugs; aftermarket bracelet with inconsistent finishing; clasp stamped with generic markings instead of Seiko markings
casebackExhibition caseback showing Cal. 6R35Exhibition caseback shows Cal. 6R35 rotor and bridges; Seiko model text and 200m rating engraved on caseback exterior; case serial on case sideMovement is not 6R35 (different architecture or different beat rate); caseback text absent or poorly engraved
Common legitimate replacements
  • Bezel inserts are a genuine Seiko service part and are commonly replaced; an original Seiko insert is fine.
  • Bracelets are frequently swapped for NATO or rubber straps and then relisted without the original bracelet.
  • Crystal is sapphire and rarely needs replacement, but mineral crystal substitutions occur on grey-market units.
Expert resources: Seiko serial number dating tools are available at seikousa.com and community sites like r/Seiko. WatchUSeek Seiko forum covers SPB143 authentication. The Seiko service center can verify Cal. 6R35 authenticity.

Authentication guide

Last reviewed June 2026

The SPB143 is a direct recreation of Seiko's 1965 diver with a 40.5mm modern case. Cal. 6R35 is the upgraded successor to 6R15 with 70-hour power reserve. The unidirectional aluminum bezel and 200m diver designation are the primary authentication anchors.

Known reproduction risks

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MEDIUM

The vintage-homage aesthetic of this reference attracts reproduction makers who source close-looking cases with incorrect calibers.

  • Crown positioned at 3 rather than 4 o'clock
  • Bezel insert that rotates bidirectionally rather than unidirectionally
  • Caseback without the Seiko S medallion
  • Movement with a different caliber code than 6R35

Dial variants by era

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EraDescriptionIdentifiers
2020 to presentSilver-and-black two-tone dial referencing the original 1965 design. Arabic numerals at 12, 6, and 9; applied indices at all other positions. Dial printing is clean with no smearing on originals.
  • Silver outer chapter ring with black inner dial
  • Large luminous applied indices with cream-tone lume consistent across all positions
  • "PROSPEX" and "AUTOMATIC" printed on the dial
  • "DIVERS 200M" designation below 12
  • Date window at 3, no magnifier

Service part flags

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Dial

Original: Silver/black two-tone. The lume on the applied indices is thick and domed. Original dials have a tight seam between the two dial zones with no visible gap.

Replacement tells
  • Flat or thin lume plots on the applied indices
  • Visible gap or misalignment between the silver and black dial zones
  • Incorrect font on the "DIVERS 200M" designation
Bezel

Original: Unidirectional rotating aluminum insert. The click action is positive with 120 clicks per revolution. The bezel insert markings are printed, not applied.

Replacement tells
  • Loose bezel click action with fewer than 120 detents per revolution
  • Ceramic insert substituted for the original aluminum
  • Printed markings that have faded unevenly, suggesting a reproduction insert
Crown

Original: Non-screw-down push-pull crown at 4 o'clock (not 3), consistent with the vintage Seiko diver design.

Replacement tells
  • Crown repositioned to 3 o'clock, which indicates a replacement case
  • Screw-down crown mechanism, incorrect for this reference
Caseback

Original: Solid stainless caseback with "DIVERS 200M" designation and Seiko S medallion in the center.

Replacement tells
  • Missing Seiko S medallion on the caseback center
  • Aftermarket display caseback
  • "200M" replaced with incorrect water resistance marking

Case back markings

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2020 to present
  • SPB143J1 reference number
  • "DIVER'S 200M" designation
  • Seiko S logo medallion in the center
  • Cal. 6R35 designation
  • Serial number encoding production year in the first digit

Movement tells

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  • Cal. 6R35 runs at 28,800 bph with a 70-hour power reserve. The upgrade from 6R15 adds 20 hours of reserve; any SPB143 that stops before 55 hours from a full wind has a worn mainspring.
  • The 6R35 is hackable and manually windable. Confirm both functions before purchase.
  • The movement is visible only via the solid caseback's engravings, not through glass. Any SPB143 with a display caseback has been modified.
Sources: Seiko Prospex SPB143 product page; Fratello Watches -- SPB143 review.

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Buying guidance

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