Summer Special: Seiko SKX007 vs Citizen NY0040, Which Diver Suits You?

Neither watch is objectively better. The Seiko SKX007 and Citizen NY0040 are close on paper: both are automatic divers with 21 jewels, both carry a 200 m original water-resistance rating, and their cases differ by only half a millimetre. The practical choice comes down to three things: strap width, crown position, and whether you want the exact movement and certification paperwork that Citizen publishes for its current NY0040 references. The SKX007 is a discontinued reference, so the comparison below treats its specifications as those given in a historical comparison rather than a current Seiko listing.

Side-by-side specifications

The table separates what each source states from what remains unconfirmed. Where a value is not stated by the cited source, the cell says so.

#	Preview	Product	Price
1		TACTICAL FROG Heimdallr Mens Automatic Watch, SKX007 Dive Watches for Men, NH36A Movement C3...	$151.99	Buy on Amazon
2		SEIKO SRPL51 Automatic Diver Watch Men's Prospex - Blue	$476.00	Buy on Amazon

Because the two watches share beat rate, jewel count and a 200 m original rating, the differences that matter in daily wear are fit, crown placement and the way each watch is documented.

Fit and daily wear

Lug width and strap choice

The most consequential difference is the lug width. The SKX007 takes 22 mm straps and the NY0040 takes 20 mm straps. A 22 mm strap will not sit correctly on a 20 mm lug, and forcing it leaves gaps that look untidy and can loosen the strap over time. If you already own straps or plan to buy several, measure your existing straps before choosing. Because Citizen has produced many NY0040 suffixes, confirm the exact variant’s lug width on the reference before buying a strap.

#1 Best Overall

TACTICAL FROG Heimdallr Mens Automatic Watch, SKX007 Dive Watches for Men, NH36A Movement C3 Luminous, 200 Meter Water Resistant, (Blue 5link)

• NH36A Movement: Powering the stainless steel watches for men is Japan 24 jewels fully automatic NH36A Movement. Assembled in Malaysia, providing precise and accurate time keeping. Power reserve can last for 41 hours. Case 42 mm x 13 mm thick. Watch weight:185 grams.
• High Quality Workmanship: The automatic watch features a 42mm brushed & polished steel case with a black ceramic bezel and wave dial with arrow hands. Scratch resistant sapphire crystal glass with anti-reflective coating on inner surface; 22 mm Width Solid 316L stainless steel bracelet is adjustable by removing or adding links and fold over clasp with safety and fine tune function. A must have Heimdallr watch for collection.
• Diving Watches: Screw down lock for water tight seal and uni-directional ceramic bezel to tell you "under" time easilly. Heimdallr mechanical watch is water resistant to 200 M(20 ATM). Suitable for professional marine activities, swimming, water sports and daily wearing.
• Luminated Watch: Green Luminious hands and hour markers are using C3 material, which can last for at least 5 hours in dark and is able to quickly absorb and store light energy in a bright environment.
• Ideal Present for Men: This striking dress watch has tremendous wrist presence while maintaining a stealthy look. Robust work of art wears exceptionally well for formal and sporty events thanks to its classy (yet modern) looks. It can be a trustworthy present choice for your father, husband or boyfriend on special occasions

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Case diameter is nearly identical on paper, but wrist shape and lug-to-lug length decide how a watch sits. Try to check the lug-to-lug measurement on a specific example before deciding, rather than relying on the diameter alone.

Crown position

The SKX007’s crown sits at 4 o’clock and the NY0040’s at 8 o’clock. Both are on the same side of the wearer’s wrist in different ways, so the feel changes with how you wear the watch. Some wearers find the 8 o’clock crown easier to avoid when pushing a sleeve or cuff. Others prefer the familiar 4 o’clock placement of the SKX line. This is a matter of preference, not a measurable advantage for either.

Bezel and crystal

The SKX007’s 120-click bezel gives finer adjustment than the NY0040’s 60 clicks, which may matter if you use the bezel for timing. Both use a mineral crystal. Neither source supports claims about relative scratch resistance, so choose on the basis of appearance and whether you want the flat crystal that the SKX007 is described as using.

Movement: identify the exact reference first

The movement is the area where a blanket answer is most likely to be wrong. The Fratello comparison describes the SKX007’s 7S26 as neither hand-winding nor hacking, which means the seconds do not reset when the crown is pulled out and the watch cannot be wound by hand. Treat that as the comparison’s description and check Seiko’s documentation for your specific caliber.

For the NY0040, the historical comparison places it in the 8200 family, but Citizen’s official page for the NY0040-09EC references caliber 8204. Movement features can differ between suffixes and generations, so do not assume the 8200 description applies to every NY0040 you find.

1. Remove the strap or look at the caseback and locate the caliber code. Seiko says its model-specific instructions are keyed to the caliber code on the caseback.
2. Note the full reference or suffix printed on the caseback or dial, such as NY0040-09EC or NY0040-50E.
3. Match that reference to the manufacturer’s official page or documentation before relying on any movement claim.
4. If you cannot read the caliber code or reference, treat the movement details in this article as unverified for that watch.

Seiko has said it began gradually discontinuing paper manuals from February 2024, so you may need to download manuals from Seiko’s website rather than expect one in the box.

Rank #2

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SEIKO SRPL51 Automatic Diver Watch Men's Prospex - Blue

• 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

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Water resistance and diver certification

Both watches were originally rated to 200 m. For the NY0040, Citizen’s official Italy page for the NY0040-50E lists 20 bar water resistance and identifies the watch as an ISO 6425 professional diver. Citizen Japan’s FAQ says its diver watches marked “DIVER’S WATCH 200m” conform to ISO 6425. According to that FAQ, the standard covers:

• timing indication
• visibility
• magnetic resistance
• thermal shock
• salt water
• impact
• water resistance
• component strength
• helium gas

For the SKX007, the ISO characterization comes from the Fratello comparison; no official Seiko product record for the SKX007 was available to confirm it. Treat the SKX007’s certification as a secondary-source claim.

A rating describes how a new watch was designed and tested. It does not show that a particular used watch still seals correctly. Gaskets age, crystals can be cracked, and crowns may have been removed and reinstalled. Before you swim or dive with either watch, have a qualified watchmaker pressure-test it. This applies to both models and is not a sign that either has a known defect.

Buying a used watch

Used prices and availability change quickly and vary by region, condition and seller, so this article does not quote them. Before you buy, check the following.

1. Confirm the reference and caliber code against the manufacturer’s documentation.
2. Measure the lug width and confirm it matches the strap you plan to use.
3. Inspect the crystal for cracks or chips, especially at the edges.
4. Check that the crown screws down and that the bezel turns with the expected clicks and no excessive play.
5. Ask whether the seller has pressure-tested the watch, and if not, budget for a test before water use.
6. Verify that dial, hands and bezel insert match the reference. Replaced parts can change the appearance and the value.

Which one to choose

• Choose the SKX007 if you already own 22 mm straps, prefer a 4 o’clock crown, want the finer 120-click bezel, and are comfortable verifying an older, discontinued watch’s condition.
• Choose the NY0040 if you want the 20 mm strap width, an 8 o’clock crown, and a current Citizen model with published ISO 6425 documentation for the NY0040-50E.
• Choose by movement only after you have confirmed the exact NY0040 suffix and caliber, because the movement details differ across references.
• Choose by fit if you can try both on: lug-to-lug length and how the case sits on your wrist will matter more than the 0.5 mm difference in diameter.

Be cautious about anecdotes that either watch is better for military use or more accurate. The sources reviewed for this comparison do not establish those claims, so this article does not rely on them.

Quick Recap

Bestseller No. 1

TACTICAL FROG Heimdallr Mens Automatic Watch, SKX007 Dive Watches for Men, NH36A Movement C3 Luminous, 200 Meter Water Resistant, (Blue 5link)

$151.99

SaleBestseller No. 2

SEIKO SRPL51 Automatic Diver Watch Men's Prospex - Blue

AUTOMATIC MOVEMENT for seamless precision in every tick of this watch; WATER RESISTANT DESIGN ensuring your watch is ready for any adventure, rain or shine

$476.00

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.