Seiko SKX vs SPB: Which Diver Should You Choose?

Quick Verdict: The Seiko SKX offers legendary value and mod potential at $300-500 used; the Prospex SPB delivers superior movement and materials at $1,000+. Choose SKX if you want a proven tool watch with customization options. Choose SPB if you want refined finishing and modern conveniences without the used market hunt.

This comparison addresses the question facing Seiko dive watch buyers in 2026: pursue a discontinued legend on the used market, or invest in its spiritual successor? Both represent Seiko's dive watch philosophy, but they target different buyers with different priorities.

Quick Comparison: SKX vs SPB at a Glance

* SKX prices as of early 2026. Excellent condition and NOS examples command higher premiums.

Movement Comparison: 7S26 vs 6R35

The movement difference represents the clearest upgrade between generations. Understanding these calibers explains much of the price gap.

Seiko 7S26 (SKX)

The Seiko 7S26 movement prioritized reliability over refinement. It lacks hacking (stopping seconds for precise time-setting) and hand-winding capability—features expected in modern automatics. This wasn't oversight but cost engineering: removing complexity reduced manufacturing costs while maintaining core reliability.

7S26 Specifications:

• Type: Automatic (self-winding only)
• Jewels: 21
• Frequency: 21,600 vph
• Power Reserve: ~40 hours
• Accuracy: -20/+40 seconds per day (factory spec)

In practice, most 7S26 movements run within ±15 seconds daily after break-in. The movement has proven essentially bulletproof over decades, with service costs remaining low due to widespread parts availability.

Seiko 6R35 (SPB)

The 6R35 represents Seiko's mid-tier automatic technology: significantly refined over the 7S26 while remaining accessible compared to Grand Seiko calibers.

6R35 Specifications:

• Type: Automatic with hand-winding
• Jewels: 24
• Frequency: 21,600 vph
• Power Reserve: 70 hours
• Accuracy: -15/+25 seconds per day (factory spec)
• Hacking: Yes

The 70-hour power reserve is the standout specification—nearly double the SKX's capability. This means the SPB continues running through a full weekend without wearing, where the SKX might stop Saturday night.

Movement Verdict

The 6R35 objectively outperforms the 7S26 in every measurable specification. Whether these improvements justify the price premium depends on how much you value hacking seconds, hand-winding convenience, and extended power reserve.

Materials and Construction

Crystal

The SKX uses Hardlex mineral crystal—Seiko's proprietary hardened mineral glass. It resists impacts better than standard mineral but scratches more easily than sapphire. Many SKX owners eventually replace it with aftermarket sapphire.

The SPB includes factory sapphire crystal with anti-reflective coating. This upgrade alone addresses the SKX's most common criticism and eliminates scratch vulnerability during daily wear.

Bezel Insert

The SKX's aluminum bezel insert shows wear over time—scratches, fading, and color shifts are common on well-used examples. Some collectors appreciate this patina; others find it unacceptable.

The SPB uses a steel bezel with painted markings rather than ceramic. While more durable than aluminum, it lacks the scratch resistance and color permanence of ceramic inserts found in higher-priced competitors.

Case Finishing

The SPB demonstrates noticeably superior case finishing: sharper brushing, cleaner polishing transitions, and more refined dial printing. The SKX's finishing is adequate but clearly reflects its lower price point.

For buyers seeking ceramic bezels and sapphire crystals at accessible pricing, third-party options exist. Brands like SKYRIM offer dive watches using proven Seiko NH35 movements with upgraded materials—sapphire crystal and ceramic bezel inserts—at $289, addressing the material limitations that both SKX and SPB share in different ways.

Size and Wearability

The SKX measures 42mm but wears smaller due to its short 46mm lug-to-lug distance. The SPB at 40.5mm with 47mm lug-to-lug actually occupies similar wrist presence. Neither overwhelms average wrists.

Thickness differs more noticeably: the SKX at 13.25mm and SPB at 13.2mm are essentially identical. Both sit prominently on the wrist—these are tool watches, not dress pieces.

The practical difference comes down to case shape. The SKX's cushion-shaped case and 4 o'clock crown create its distinctive silhouette. The SPB's more conventional round case reads as refined rather than rugged.

Value Analysis

SKX Value Proposition

At original retail (~$200), the SKX offered unmatched value: ISO-certified dive capability, automatic movement, and proven reliability at a price point Swiss brands couldn't match. Current used pricing ($300-500) still represents reasonable value, though the gap has narrowed.

SKX Value Factors:

• Proven 23-year production track record
• Massive aftermarket modification ecosystem
• Simple, serviceable movement ($50-100 service cost)
• Rising collectibility as supply decreases
• Potential appreciation over time

SPB Value Proposition

At $1,000-1,300, the SPB competes against serious alternatives: Tudor Black Bay, Oris Aquis, and Longines HydroConquest. It represents Seiko's premium dive value before jumping to Grand Seiko pricing.

SPB Value Factors:

• Superior 6R35 movement with 70hr reserve
• Factory sapphire crystal (no aftermarket upgrade needed)
• Full warranty and authorized service network
• No used market authentication concerns
• Modern production quality consistency

Value Verdict

Dollar-for-dollar, the SKX delivers more watch per dollar—if you can find a good example and don't mind used market risks. The SPB offers peace of mind and superior specifications for buyers who prefer new purchases with full warranty support.

Mod Potential and Customization

This comparison heavily favors the SKX. Its standardized case design spawned the largest watch modification community in the hobby.

SKX Modification Options

• Crystal upgrades (sapphire, double-domed mineral)
• Bezel insert replacements (ceramic, sapphire, lumed)
• Chapter ring options (dozens of styles)
• Dial replacements (hundreds of designs)
• Hand set options (countless combinations)
• Movement upgrades (NH36 adds hacking/winding)

The SKX essentially functions as a platform for custom watch building. Enthusiasts can transform a basic SKX007 into something entirely personal.

SPB Modification Limitations

The SPB's different case architecture limits modification options. While some aftermarket parts exist, the ecosystem is fractional compared to SKX. Most SPB owners keep their watches stock.

For buyers interested in customization without DIY modification, brands building on Seiko movement platforms offer pre-configured options. The mod watch market provides dial colors, hand styles, and bezel variations that factory Seiko doesn't offer.

Which Should You Choose?

Choose the SKX If:

• Budget Priority: You want maximum dive watch capability at $300-500
• Modification Interest: You plan to customize dial, hands, bezel, or crystal
• Historical Connection: You value owning a piece of dive watch history
• Tool Watch Philosophy: You want a beater that can take abuse without worry
• Investment Perspective: You believe discontinued SKX values will continue rising

Choose the SPB If:

• Modern Features: You want hacking, hand-winding, and 70-hour reserve
• New Purchase Preference: You prefer full warranty and no authentication concerns
• Superior Materials: Factory sapphire and better finishing matter to you
• Single Watch Collection: This will be your primary or only automatic watch
• Refined Aesthetic: You prefer polished over rugged appearance

Consider Alternatives If:

• Budget Under $300: The Seiko SRPD series offers 4R36 movement with hacking/winding at $250-300, though with 100m (not ISO dive) rating
• Ceramic Bezel Priority: Neither SKX nor SPB offers ceramic; third-party options using Seiko movements address this at various price points
• GMT Functionality: Neither offers dual-timezone; brands like SKYRIM provide GMT function via NH34 movement at $295-345, combining Seiko reliability with travel functionality

Buying Guide

Buying a Used SKX

Where to Buy:

• Watch forums (WatchUSeek, Reddit r/Watchexchange)
• eBay with authentication service
• Chrono24 with buyer protection
• Local watch meetups for in-person inspection

What to Check:

• Movement function (request video of seconds sweep)
• Bezel action (clean clicks, no play)
• Crystal condition (Hardlex scratches easily)
• Lume strength (faded lume suggests age/water intrusion)
• Caseback authenticity (correct serial number format)
• Crown threading (should screw down smoothly)

Red Flags:

• Unusually low prices
• Vague seller histories
• Missing or incorrect serial numbers
• Non-original parts without disclosure

Buying an SPB

Purchase from authorized Seiko dealers to ensure warranty coverage. Gray market pricing may be lower but risks warranty issues. Key SPB models:

• SPB143: Black dial, classic diver aesthetic (~$1,100)
• SPB147: Blue dial variant (~$1,100)
• SPB149: Green "Sumo" inspired (~$1,200)
• SPB185: 1965 Diver reinterpretation (~$1,300)

FAQ

Is the Seiko SKX still worth buying in 2026?

Yes, if you find a good example at fair pricing ($300-450 for used, $500-700 for excellent/NOS). The SKX offers genuine dive capability, proven reliability, and unmatched modification potential. However, at inflated prices above $600 for standard used examples, the value proposition weakens against new alternatives.

Why did Seiko discontinue the SKX?

Seiko replaced the SKX with the SRPD series in 2019, upgrading to the 4R36 movement while repositioning the product line. The decision reflected manufacturing modernization—the 7S26 design dated to the 1990s. The SRPD lacks ISO dive certification, suggesting Seiko shifted focus from tool watch to lifestyle accessory at this price point.

Is the SPB worth the premium over SRPD?

The SPB's $800+ premium over SRPD buys: superior 6R35 movement (70hr vs 41hr reserve), sapphire crystal, ISO dive certification, and refined finishing. If these specifications matter to your use case, the premium is justified. If you're primarily desk diving, the SRPD delivers 80% of the capability at 25% of the price.

Can I upgrade an SKX to match SPB specifications?

Partially. You can add sapphire crystal ($30-50) and upgrade the movement to NH36 ($40-60 + labor) to gain hacking and hand-winding. However, you cannot match the 6R35's 70-hour reserve, and case finishing differences remain. A fully upgraded SKX costs $400-600 total and approaches but doesn't equal SPB capability.

Which holds value better: SKX or SPB?

Currently, the SKX appreciates while the SPB depreciates normally. Discontinued SKX prices have risen 50-100% since 2019 and continue climbing. The SPB, as a current production watch, loses 20-30% immediately after purchase. For investment consideration, the SKX has momentum; for wearing without value concern, both serve equally well.

Conclusion

The SKX vs SPB decision ultimately reflects different buyer priorities. The SKX offers proven reliability, legendary status, and unmatched customization potential at accessible used pricing—ideal for enthusiasts who enjoy the hunt and appreciate modification culture. The SPB delivers modern movement technology, superior materials, and warranty security for buyers who prefer new purchases with refined finishing.

Neither choice is wrong. The SKX defined affordable dive watches for a generation; the SPB continues that philosophy with contemporary improvements. Choose based on whether you prioritize heritage and customization (SKX) or specifications and convenience (SPB).

For those seeking a middle path—Seiko movement reliability with upgraded materials at SKX-level pricing—the mod watch market offers alternatives worth exploring. Brands building on genuine Seiko NH35 calibers deliver sapphire crystals and ceramic bezels at $289-349, addressing material limitations without the used market complexity or SPB premium.