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The Seiko Bullhead 6138-0040 is a vintage automatic chronograph distinguished by its crown and chronograph pushers at the top of the case. Its 6138 movement records elapsed time on 30-minute and 12-hour registers alongside chronograph seconds. For a buyer, the key questions are less about a universal price or guaranteed originality—neither is established by the available listings—than about the condition, function and parts of the particular watch.
What makes the Seiko 6138-0040 a Bullhead?
The nickname describes the control layout: the crown and chronograph pushers sit at the top of the case rather than along its right side. A collector review suggests this positioning may help reduce accidental operation of the pushers, but it is not documented as Seiko’s official reason for the design. The arrangement gives the watch a distinctive silhouette and makes the controls easy to identify at a glance. Fratello’s collector review discusses the case and controls.
What does the 6138 movement do?
Seiko places the 6138 in its automatic chronograph history. The company’s account traces the line to the 1964 Crown Chronograph, a manual-wind, one-pusher chronograph, and describes the later 6138 as adding 30-minute and 12-hour totalizers. Seiko also calls the caliber a foundation of its continuing automatic chronograph line. Seiko’s chronograph history provides that context.
Seiko Service USA’s circa-2002 technical sheet for the 6138A specifies automatic winding with auxiliary hand winding, a day-date calendar, chronograph seconds, and 30-minute and 12-hour recording. It gives the 6138A a rate of 21,600 vibrations per hour. That sheet describes the 6138A; it should not be treated as a complete specification for every 6138 variant or every watch carrying a Bullhead dial and case. Seiko Service USA’s 6138A technical sheet has the movement details.
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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.
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- 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.
How large is the 6138-0040?
A 2023 Jones & Horan auction catalogue lists its 6138-0040 example as 43 mm by 46 mm to the lug tips, with 20 mm lug width. Those are measurements for that lot, not a guarantee that every surviving example measures identically; case wear, replacement parts and measurement methods can affect comparisons. The catalogue also describes a 21-jewel 6138B, day-date at 6, and minute and hour registers for its listed watch. Jones & Horan’s 2023 listing records those example-specific details.
What should you check before buying one?
These are decades-old watches, so inspect the individual example rather than assuming all Bullheads are original or in comparable condition. Fratello’s collector review notes aftermarket parts, damaged bezels, scratched cases and crystal wear among concerns seen in old examples; it does not establish how common those issues are. A catalogue description is also a description of one lot, not proof that every component on another watch is factory-correct.
Rank #2
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- Originality: Ask whether the dial, hands, bezel and bracelet are original, replaced or refinished. Request clear photographs and a written account of any known substitutions.
- Case: Look for deep wear, sharpness of edges and signs of refinishing. A polished case may look cleaner but can lose its original shape.
- Crystal: Check for scratches, chips or cracks that obscure the dial, and ask whether a replacement is documented.
- Calendar and chronograph: Confirm that the day-date changes and that the chronograph starts, stops and resets correctly. A seller’s statement that a watch runs is not the same as evidence that every function works.
- Service history: Request invoices or other documentation, including the date and scope of work. If there is no record, treat service condition as unknown rather than assuming the watch is ready for regular use.
- Parts disclosure: Ask the seller to identify replacement components and distinguish known facts from guesses.
The sources here do not establish a reliable current market-price range, production total or survey of originality and condition. An individual auction result should not be read as a market average.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What strap or replacement parts fit?
A 20 mm straight-end strap is a plausible starting point: the 2023 auction catalogue gives 20 mm lug width for its example, and a 2026 Watchura guide recommends straight-end 20 mm straps for the reference. Those sources do not guarantee fit on every watch sold as a 6138-0040. Measure the actual lug width and check the end shape and clearance before ordering. Watchura’s 2026 strap guide gives its recommendation.
Rank #3
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A parts guide for the 6138-0040 documents a mineral crystal (part 340W14GN), along with categories including a crown, gaskets and pusher. This establishes that such part references are documented, not that a retailer currently has them in stock or that an item will fit every example. Confirm the exact reference and compatibility with a watchmaker or specialist before purchasing. The 6138-0040 parts guide is a reference for those categories.
Quick Recap
Best Value
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- 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.
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Rank #4
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