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The Seiko Prospex Baby Tuna SRP655K1 and SRP653K1 are 200 m automatic divers built around the same 4R36 movement and oversized, shrouded case. The main difference is the colorway: the SRP655K1 is black with red-circled indexes and a black strap; the SRP653K1 is blue with white-circled indexes and a blue strap. At 50.2 mm across, fit—not the movement—is the central question for most buyers.
SRP655K1 vs. SRP653K1: what changes?
| Reference | Dial and index accents | Strap | Mechanical difference established? |
|---|---|---|---|
| SRP655K1 | Black, with red-circled indexes | Black | No; the sources identify the same 4R36 movement |
| SRP653K1 | Blue, with white-circled indexes | Blue | No; the sources identify the same 4R36 movement |
The 2015 Monochrome review presents the two as color variants, not as different technical packages. The retailer listings likewise identify both as stainless-steel, 200 m diver models with silicone straps and Hardlex glass. Choose between them by appearance and by the individual watch’s condition, completeness, seller warranty, and return terms.
How the Baby Tuna is designed
In Brice Goulard’s April 9, 2015 review, Monochrome describes a scallop-shaped stainless-steel central case, curved caseback, and protective shroud covering the case and bezel. The shroud still leaves access to grip the bezel, which has deep grooves and a 60-minute scale. The bezel rotates in one direction.
The large hands and indexes use luminous material; the markers include dots and triangles rather than only straight baton shapes. The design prioritizes conspicuous underwater-style legibility and protection over a discreet profile. Seller listings specify a screw-down crown, screw caseback, and Hardlex glass. The available sources do not establish ISO certification, so the 200 m rating should not be treated as proof of such certification.
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- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
4R36 movement and published specifications
Both references use Seiko’s 4R36 automatic movement. Monochrome’s 2015 review reports hand winding, day/date display, a 41-hour power reserve, 24 jewels, and a rate of 21,600 beats per hour. The retailer listing for the black reference also gives a 41-hour reserve. These are published specifications, not results of independent testing.
- Movement: Seiko 4R36 automatic
- Functions: hand winding and day/date display
- Reported reserve: 41 hours
- Reported jewels and rate: 24 jewels and 21,600 beats per hour, as listed in Monochrome’s 2015 review
- Water resistance: 200 m, as stated by the review and retailer listings
Is the 50.2 mm case too big?
Monochrome reports a 50.2 mm case diameter and calls the watch very large, suggesting it is more at home over diving gear than with formal clothing. That diameter is a substantial wrist presence and should be treated as a real fit constraint, not a minor specification.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Comfort impressions vary. Monochrome’s 2015 reviewer says the curved back, soft silicone strap, and lack of protruding lugs help it sit comfortably. Owner reviewer Yeoman, writing in June 2015, says it wore low when tightened sufficiently and notes that the large case could leave excess strap tail. He measured his watch at 50 mm diameter, 12.5 mm thick at 3 o’clock, 16.5 mm at 11 o’clock, and 22 mm lug width. Those are his measurements; measurement methods and points differ, which helps explain the small diameter discrepancy.
If possible, try one on or compare its dimensions with a watch you already wear. Wrist circumference alone cannot guarantee fit: case shape, strap adjustment, and where the watch sits all matter. If the strap tail or the width feels distracting, the other colorway will not solve that—the references share the oversized format.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Price and availability
Monochrome reported a European price of €629 including tax in its April 2015 review. That is historical launch-era context, not a current price. On October 4, 2026, the checked SEIKO AUS Watches page for the SRP655K1 displayed US$825 and out of stock; its SRP653K1 page displayed a US$455 sale price and US$746 regular price, also out of stock. These page prices were not validated transactions and do not establish either model’s current market value.
These are legacy references, so evaluate any listing as a specific used or remaining-stock watch rather than assuming a standard current retail price. Check the watch’s condition, whether the box and papers are included, service history, warranty coverage, and return policy. Confirm availability directly with the seller before relying on a listing.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
What to check before buying
- Confirm the reference on the watch and listing: SRP655K1 is black; SRP653K1 is blue.
- Inspect case, shroud, bezel action, crown, crystal, hands, and dial for condition consistent with the seller’s description.
- Ask whether the day/date and winding functions operate as expected; a stated specification is not a guarantee about an individual watch’s condition.
- Check strap condition and whether the original strap is included. Yeoman reports a 22 mm lug width, but confirm compatibility before ordering a replacement strap.
- Review seller standing, warranty, included parts, and return terms before purchase.
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.
