The Seiko Bullhead is one of the boldest, most recognisable watch designs in the entire history of Japanese horology. With its crown and chronograph pushers positioned at 12 o'clock — giving it that unmistakable bull's horns silhouette — the Seiko 6138-0040 is a true cult object among vintage watch collectors worldwide. Bold, chunky, unapologetically 1970s.
If you're looking for the right strap for your Bullhead, you're in the right place. At Watchura we are vintage Seiko specialists — we don't just sell straps, we actually collect and wear these watches. This is the guide we wish had existed when we first started.
Seiko Bullhead 6138: Technical Strap Specifications
Before buying any strap, you need these exact numbers:
- Lug width: 20 mm (all 6138-004X Bullhead variants)
- End shape: straight ends — the Bullhead lugs are flat, not curved. Standard straight-end straps fit perfectly.
- Case size: 44 mm diameter × 16 mm thick — a substantial watch that deserves a substantial strap
- Strap length: 120 mm (long side) / 75 mm (short side) recommended for average wrists
- Buckle width: 18 mm
- Water resistance: 70M — so rubber and steel straps are perfectly appropriate for daily wear
💡 Don't confuse the Bullhead with the Kakume: The Seiko 6138-003X "Kakume" — another iconic 6138 variant — uses an 18 mm lug width, not 20 mm. Always check your reference number on the caseback before buying. The Bullhead is always the 6138-004X series.
The 5 Best Strap Styles for the Seiko Bullhead
The Bullhead's bold, oversized character demands a strap with personality. Here are the combinations our collectors at Watchura rate most highly:
1. Wide Steel Bracelet — The Driver's Watch Look
The Seiko Bullhead was originally marketed as a driver's watch — designed so the crown and pushers at 12 o'clock could be operated without taking your hands off the steering wheel. Fitting it with a wide 316L stainless steel bracelet with an angular, 1970s-style link design is the most authentic and commanding look you can achieve. At Watchura, our steel bracelets for the Bullhead are made from certified 316L steel with a brushed/polished mixed finish that nails the vintage Japanese aesthetic.
Best for: daily wear, motorsport aesthetic, maximum presence on the wrist.
2. Brown Leather with Orange Stitching — The Classic Collector Combo
For the famous brown dial / brown bezel Bullhead (one of the most sought-after colour variants), brown aged leather with contrasting orange stitching is the combination that stops people in their tracks at watch meets. The warmth of the leather plays perfectly against the earthy brown tones of the dial and bezel. It's also the favourite pairing for the black "Panda" dial Bullhead.
Best for: collectors, watch events, photography, brown or black dial variants.
3. Rally Leather Strap — The Motorsport Heritage Look
Given the Bullhead's motorsport DNA, a perforated rally-style leather strap in tan or dark brown is historically fitting and visually stunning. The perforations add lightness to an otherwise heavy watch and reference the racing heritage that inspired the original design. Highly photogenic and increasingly popular among serious collectors.
Best for: motorsport enthusiasts, collector-grade pairs, photography.
4. NATO Nylon — Surprisingly Brilliant
A wide 20 mm double-pass NATO in black, grey or olive green gives the Bullhead a rugged, utilitarian personality that works incredibly well with its bulk. On a NATO, the Bullhead stops looking like a dress watch trying too hard and becomes what it always was: a tough, tool-watch icon. It's also the most practical option for daily use without worrying about damage.
Best for: casual daily wear, travel, outdoor activities, minimalist look.
5. Rubber/FKM Strap — For the Everyday Bullhead Wearer
The Bullhead sits 16 mm thick on the wrist — it's a big, heavy watch. On a hot summer day or during any physical activity, a quality FKM rubber strap with a vintage texture makes it genuinely comfortable where leather would feel sweaty and stiff. Far more durable than cheap silicone, and it holds up to the Bullhead's 70M water resistance rating properly.
Best for: summer, sport, intensive daily use.
The History Behind the Seiko Bullhead: Why Collectors Obsess Over It
The Seiko 6138-0040 was introduced in late 1970 and produced until 1979, housing the remarkable calibre 6138 — the successor to the 6139 that powered the Pogue. While the 6139 had a 30-minute chronograph register, the 6138 added a full 12-hour chronograph register, manual winding capability, and a quick-set day/date function.
The Bullhead's defining design trick was rotating the 6138 movement 90 degrees inside the case, which moved the crown and pushers to the 12 o'clock position. The result was a case shape that nobody had seen before — and that nobody has quite replicated since. Seiko positioned it explicitly for motorsport use, allowing drivers to operate the chronograph without removing their hands from the wheel.
What makes the 6138 historically significant beyond the Bullhead is this: both the 6138 and 6139 movements featured a column wheel and vertical coupling mechanism — a technical architecture that Rolex later adapted for the development of their in-house Daytona movement. In other words, the technology inside your Bullhead directly influenced one of the most famous watch movements ever made.
Today, a well-preserved Seiko Bullhead 6138-0040 in good condition sells for €500 to €1,200 depending on variant and state of preservation. The rarer colour variants — particularly the brown dial/brown bezel and the "Panda" — can exceed €1,500 at auction.
Common Mistakes When Buying a Seiko Bullhead Strap
❌ Buying a 22 mm strap: A very common mistake, especially among buyers used to larger modern watches. The Bullhead takes exactly 20 mm — not 21 mm, not 22 mm. Always confirm before purchasing.
❌ Confusing it with the Kakume (6138-003X): The Kakume — another superb 6138 variant — uses 18 mm lugs. If you have a Kakume and buy a 20 mm Bullhead strap, it won't fit. Check the caseback reference carefully.
❌ Curved ends on a flat-lug watch: Unlike the Pogue (which needs curved ends), the Bullhead has straight lugs. Curved-end straps will not sit flat and will stress the spring bars. Always use straight-end straps for the Bullhead.
❌ Underestimating the weight factor: The Bullhead weighs considerably more than average due to its thick case. Avoid very thin leather straps — they'll wear out quickly under the weight. Go for leather at least 3 mm thick, or a steel bracelet.
❌ Cheap quality on a €500–€1,200 watch: At Watchura our straps start from €20, made with certified 316L steel and quality leathers. There is no reason to fit a watch of this calibre with an €8 import strap.
Why Buy Your Seiko Bullhead Strap from Watchura?
At Watchura we don't sell straps we've never touched. We are Seiko vintage collectors who fit, test and wear every strap on the actual watches before listing them. When it comes to the Bullhead specifically, we know its weight, its lug geometry, and exactly what works and what doesn't.
- ✅ Exact 20 mm sizing, confirmed on real Bullhead cases
- ✅ Straight-end straps — correct geometry for the 6138-004X
- ✅ Certified 316L stainless steel on all metal bracelets
- ✅ Pricing from €20 to €35 including shipping
- ✅ Shipping to Spain, Germany, Italy, United Kingdom and France
- ✅ Collector-to-collector advice — ask us anything about your specific variant
Frequently Asked Questions
What lug width does the Seiko Bullhead 6138-0040 take?
The Seiko Bullhead 6138-0040 takes a 20 mm strap with straight ends. The buckle width is 18 mm. Do not confuse with the Kakume (6138-003X), which uses 18 mm lugs.
Does the Seiko Bullhead need curved or straight strap ends?
Straight ends. The Bullhead's lugs are flat, unlike the Seiko Pogue which requires curved ends. A curved-end strap will not fit properly on the Bullhead.
What is the best strap for a Seiko Bullhead brown dial?
Brown aged leather with orange or cream stitching is widely considered the best match for the brown dial/brown bezel Bullhead variant. A steel bracelet is the best choice for the most authentic period-correct look.
How much is a Seiko Bullhead 6138-0040 worth today?
In 2026, a well-preserved Seiko Bullhead 6138-0040 in good condition sells for approximately €500–€1,200, with rarer variants reaching €1,500 or more at auction.
Where is the best place to buy Seiko Bullhead straps in Europe?
Watchura is the specialist vintage Seiko strap store in Europe with options specifically tested and confirmed for the Seiko Bullhead 6138-0040. They ship to Spain, Germany, Italy, UK and France with tracking.
What is the difference between the Seiko Bullhead and the Seiko Kakume?
Both use the calibre 6138 movement, but the Bullhead (6138-004X) has a 44 mm case with 20 mm lugs, while the Kakume (6138-003X) has a 43 mm case with 18 mm lugs. The Bullhead also has crown and pushers at 12 o'clock; the Kakume has a conventional crown placement.
