They are not both PADI watches. Seiko identifies the 1965 Heritage Diver’s Watch SPB501 as a Prospex–PADI special edition. SRPL51 is listed as a blue-dial Prospex automatic diver, without PADI designation in the official listings consulted. This is a specification-based first look, not a hands-on review or timing, lume, or underwater test.
What separates the SPB501 and SRPL51?
The biggest differences are movement, power reserve, case dimensions, crystal, and water-resistance rating. SPB501 uses Seiko’s 6R55 movement and is rated to 300 metres; SRPL51 uses the 4R35 and is rated to 200 metres. SPB501 is also smaller across the wrist but longer from lug to lug, while SRPL51 is thinner and uses Hardlex rather than sapphire.
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| Specification | Seiko Prospex SPB501 | Seiko Prospex SRPL51 |
|---|---|---|
| Official identity | 1965 Heritage Diver’s Watch PADI Special Edition | Prospex automatic diver; blue dial in Seiko’s US descriptive copy |
| Movement | Caliber 6R55, automatic with manual winding | Caliber 4R35, automatic with manual winding |
| Published power reserve | Approximately 72 hours (three days), Seiko Watch Corporation listing accessed 2026 | Approximately 41 hours, Seiko Boutique Hong Kong listing accessed 2026 |
| Case size | 40.0 mm diameter; 46.4 mm lug-to-lug; 13.0 mm thick | 41.7 mm diameter; 12.3 mm thick; lug-to-lug not stated in the consulted listing |
| Crystal | Curved sapphire with anti-reflective coating on the inner surface | Hardlex |
| Water resistance | 300 m / 1,000 ft diver’s | 200 m / 660 ft diver’s |
| Dial and supplied band | Emerald-green gradient dial; stainless-steel bracelet plus an additional fabric strap made from nylon upcycled from discarded fishing nets | Blue dial; stainless-steel construction and bracelet in the consulted listing |
| Weight | 174.0 g | 170.0 g |
| Displayed price | USD 1,650 on Seiko’s US page accessed 2026 | HK$4,680 on Seiko Boutique Hong Kong accessed 2026 |
The prices are shown in different markets and currencies, so they are not a direct retail comparison. Local pricing, stock, taxes, and warranty terms should be checked before purchase.
SPB501: the actual PADI special edition
Seiko describes SPB501 as “A special edition symbolizing the partnership between Prospex and PADI.” Its green gradient is presented as an interpretation of underwater light and ripples. The package includes a stainless-steel bracelet and a fabric strap made from nylon upcycled from discarded fishing nets, woven using the Seichu technique.
#1 Best Overall
- 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
Movement and dimensions
The 6R55 is automatic with manual winding and has a published accuracy range of +25 to −15 seconds per day. Seiko lists 24 jewels and an approximately 72-hour reserve. The 40.0 mm case measures 46.4 mm lug to lug and 13.0 mm thick, with 20 mm between the lugs.
Diver specifications
SPB501 has a unidirectional bezel, screw-down crown, screw-down case back, curved sapphire crystal with inner anti-reflective coating, and a 300 m / 1,000 ft diver’s rating. These are manufacturer specifications, not results from an independent pressure, timing, or underwater test.
Rank #2
- STAINLESS STEEL CASE built to endure with style, making this watch your perfect daily companion
- AUTOMATIC MOVEMENT for seamless precision in every tick of this watch
- SCRATCH-RESISTANT CRYSTAL to maintain a pristine look even with daily wear and tear on your watch
- LUMINESCENT HANDS for effortless readability in low-light conditions, ensuring you never miss a moment with this watch
- WATER RESISTANT DESIGN ensuring your watch is ready for any adventure, rain or shine
Bracelet adjustment
Its clasp provides six adjustment steps of approximately 2.5 mm each—about 15 mm of total fine adjustment, according to Seiko. The stated 20 mm lug width also defines the fit for any replacement strap; compatibility should be verified for the specific strap and spring bars.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsSRPL51: a blue Prospex diver, not identified as PADI
The consulted official SRPL51 listings present a blue-dial Prospex automatic diver. They do not identify it as a PADI edition. That distinction matters if the partnership branding or special-edition provenance is the reason you are shopping.
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
- 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
Movement and dimensions
Seiko Boutique Hong Kong lists caliber 4R35, automatic with manual winding, 23 jewels, and an approximately 41-hour reserve. The case is 41.7 mm in diameter and 12.3 mm thick. The same coherent specification table does not state a lug-to-lug measurement, so no figure should be inferred from the diameter.
Diver specifications
SRPL51 has a date display, screw-down crown, screw case back, unidirectional rotating bezel, secure-lock clasp with push-button release and extender, Hardlex crystal, and a published 200 m / 660 ft diver’s rating. Those figures come from Seiko’s regional product listing and are not comparative real-world test results.
Rank #4
- KHAKI GREEN DIAL: this rugged sports watch features a khaki green dial patterned to mirror the shape of the bezel’s edge, with Lumibrite dial indicator hands and markers for low light and a magnified day/date calendar
- BLACK BEZEL: this versatile men’s watch features a black ceramic unidirectional bezel with distinctive scalloped edging, for elapsed timing
- AUTOMATIC & MANUAL: SRPE05 automatic watches for men power up with your natural movements, and feature the ability to wind manually, with 41 hours of reserve power
- WATER-RESISTANT: these rugged stainless steel dive watches for men feature a khaki green silicon strap, and are both stylish and robust, following ISO standards for scuba, and are water-resistant to 200 meters
- 4R36 CALIBER: equipped with the reliable 4R36 caliber, these precise men’s wrist watches ensure the most accurate timekeeping
Which model fits your priorities?
Choose SPB501 if you want
- The explicitly documented Prospex–PADI special edition.
- A smaller 40.0 mm diameter and 46.4 mm published lug-to-lug measurement.
- Curved sapphire rather than Hardlex.
- A roughly three-day reserve that can keep running through a weekend off the wrist.
- A 300 m / 1,000 ft diver’s rating.
- The green underwater-inspired dial and included upcycled-fishing-net fabric strap.
Choose SRPL51 if you want
- A blue Prospex diver without relying on PADI-edition designation.
- A thinner 12.3 mm case.
- A lower published price in its Hong Kong market listing, while recognizing that it cannot be compared directly with the US-dollar SPB501 figure.
- A conventional 4R35-powered automatic with date display and approximately 41 hours of reserve.
What the published specifications cannot tell you
No independent wear test, measured timekeeping result, lume test, or side-by-side underwater test was established for this comparison. The accuracy, reserve, water-resistance, dimensions, weights, and clasp details above should therefore be read as Seiko’s published specifications. Wrist comfort, bezel feel, bracelet articulation, visual legibility, and actual timekeeping require handling the watches or consulting a documented independent test.
Buying and availability checks
- Confirm that you are viewing the correct reference: SPB501 is the PADI special edition; SRPL51 is the separate blue Prospex diver.
- Check the local Seiko site or authorized retailer for current price, stock, taxes, and warranty coverage. The displayed USD 1,650 and HK$4,680 figures belong to different markets and may change.
- For SPB501, confirm whether the bracelet, additional fabric strap, and clasp-adjustment hardware are included in the package in your market.
- If buying an alternate strap, match the stated 20 mm SPB501 lug width and verify end-link, spring-bar, and diver-extension compatibility.
The Bottom Line
SPB501 is the genuine PADI special edition, with the stronger 6R55 movement, approximately 72-hour reserve, sapphire crystal, and 300 m rating. SRPL51 is a thinner, blue-dial Prospex diver with a 4R35, approximately 41-hour reserve, Hardlex, and 200 m rating. The better choice depends on whether the PADI identity and upgraded specifications justify SPB501’s market-specific price for you.
Quick Recap
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.
