Lug width is the single number - 18mm, 20mm, 22mm - that determines whether a strap fits your watch. Get it right and the strap slides in without forcing; get it wrong and you’ll spend money on a strap you can’t use. Despite being stamped on almost every strap package, it’s rarely explained. The number refers to the gap between the lugs on your watch case, not the width of the strap itself - though the two must match.
This comes up constantly at our workshop. Customers arrive with a strap that’s 2mm too wide or a buckle that overhangs the edge of the case. The measurement takes five seconds with calipers; the shopping mistake takes weeks to undo. This guide covers everything you need to know before buying a replacement strap.
What Is Lug Width?
The lugs are the four metal protrusions extending from the top and bottom of the watch case that hold the spring bars - the thin pins the strap attaches to. Lug width is measured across the interior gap between the two lugs on the same side of the case, at the point where the strap meets the case. It’s always expressed in millimetres and is always an even number: 16, 18, 20, 22, 24mm. The strap must match this number exactly - a 20mm strap will not slide into an 18mm gap, and an 18mm strap will rattle loosely in a 20mm gap.
The measurement point is the interior of the lug gap - between the inner faces of the lugs at the spring bar position - not across the outside of the lugs or across the case. Measuring the case width or the outer span of the lugs gives you a different, larger number.
How to Measure Lug Width
Use Digital Calipers
The most accurate method. Open the caliper jaws and measure the inside of the lug gap - the distance between the inner faces of the two lugs at the spring bar position. If you don’t have calipers, a jeweller’s ruler laid inside the gap works for most standard sizes.
Don’t Measure the Case Width
The case width - the full diameter or width of the watch body - is a different measurement. Measuring across the outside of the lugs or across the case gives you the wrong number. Measure only the interior gap where the strap sits.
Check the Original Strap
The simplest method: look at the original strap or bracelet that came with the watch. The width is usually printed on the back of the buckle or stamped on the clasp. If the strap is worn but still attached, it’s always the right size - read it directly.
Look It Up by Model
Every major watch has its lug width listed in the specs. Search “[brand] [model] lug width” or check the manufacturer’s website. Common references: Seiko 5 (22mm), Casio F-91W (18mm), Casio G-Shock GA-100 (16mm), Citizen BJ Series (20mm), Seiko Prospex dive models (22mm).
Common Lug Widths - Reference Guide
Most watches fall into one of five standard sizes. The table below covers the sizes you’re most likely to encounter with watches sold in Albania.
| Lug Width | Typical Watches | Notes |
|---|---|---|
| 16mm | Casio G-Shock GA-100, smaller dress watches, some women’s models | Less common; fewer aftermarket strap options |
| 18mm | Casio F-91W, A168, slim field watches, most women’s watches | Very common; wide selection in leather and NATO |
| 20mm | Seiko 5 (most models), Citizen quartz, Casio Edifice, dress watches | Most popular worldwide; widest aftermarket choice |
| 22mm | Seiko Prospex, larger tool and dive watches, Casio Protrek | Standard for sports and dive watches |
| 24mm | Large dive and expedition watches | Fewer aftermarket choices; mostly leather and rubber |
Strap Width vs Buckle Width
Most straps are listed with two numbers - for example “20/16”. This means the strap is 20mm at the lug end (where it attaches to the watch) and tapers to 16mm at the buckle end. The first number must match your lug width. The second number affects how the buckle sits on your wrist but doesn’t need to match any watch measurement - it’s a comfort and style choice.
Always match the first number to your lug width. A 20mm strap with a 16mm tail is correct for a 20mm watch. A 20mm strap with an 18mm tail is also fine - the difference is in how the buckle looks and how much overlap the keeper has. Neither combination is wrong; it’s purely a matter of preference.
What If the Strap Fits the Lug Width but Looks Wrong?
Strap fit is about more than lug width. The strap thickness at the lug end must also fit the gap depth - how deep the spring bar sits in the lug. Thick leather on a shallow lug gap will push the strap away from the case and prevent it from lying flat. If a strap is the right width but won’t lie flush or the keeper barely reaches, the strap is too thick - not the wrong width.
Two other factors beyond lug width affect fit: lug curvature (straight-end vs curved-end straps - some cases require a curved-end strap to sit flush against the case) and springbar diameter (thicker springbars for heavier straps, thinner for dress straps). If the strap sits right but the springbar doesn’t click into place, the springbar is too thick for that particular lug hole. Bring the watch in and we’ll fit the right combination before you pay.
Do Metal Bracelets Follow the Same Sizing?
Standard leather, NATO, and rubber straps follow the lug width system exactly. Metal bracelets do not - they are model-specific and sized for a particular case. A Seiko bracelet won’t fit a Citizen case even if both have 20mm lug spacing, because the end-link geometry is different. If you want to restore an original metal bracelet or need a replacement, source the correct reference number from the manufacturer or bring the watch to us for identification.
Avoid “universal” metal bracelets marketed to fit any 20mm watch. The endlinks will be generic and will either rattle in the lug gap or press against the case. They look wrong and the springbars they rely on are typically undersized for bracelet weight. For metal, use model-specific bracelets - or switch to a quality leather, NATO, or rubber strap instead.
Frequently Asked Questions
Can I use a 20mm strap on a watch with 18mm lugs?
No. The strap will physically not fit - it’s 2mm too wide to slide into the lug gap. You must match the lug width exactly. Forcing it will damage the lug edges or bend the springbars.
Is lug width the same as band width?
At the lug end, yes - the strap width there equals the lug width. But most straps taper toward the buckle, so the buckle end is narrower. When a package says “20mm strap” it means 20mm at the lug end, which is the dimension that matters for fit.
Why does my “20mm strap” feel loose in the lug gap?
Some aftermarket suppliers cut straps slightly narrow - often 19.5mm - so they fit more easily during assembly. If the strap has side play inside the lug gap, it’s an undersized cut. Quality straps are cut to true size. When in doubt, try a brand-name strap in the same size.
Can I measure lug width without calipers?
Yes. Lay a millimetre ruler inside the lug gap and read the measurement. Alternatively, the original strap usually has its width stamped on the back of the clasp or printed on the strap tail near the buckle - this is always reliable.
Do you stock straps at the workshop in Durrës?
Yes. We keep leather, NATO, and rubber straps in 18mm, 20mm, and 22mm. We measure your lug width on arrival and fit the strap while you wait - no appointment needed, open Monday to Saturday.
Bring Your Watch - We Measure and Fit for Free
Not sure of your lug width? Don’t guess. Bring the watch to Iglisi Watch in Durrës and we’ll measure it on the spot. We carry leather, NATO, and rubber straps in the most common sizes and fit them while you wait. Open Monday to Saturday, no appointment required. Send us a WhatsApp photo of your watch if you want a size confirmed before making the trip.
Rruga Aleksander Goga · Durrës 2001 · Albania · +355 67 636 0510
Published by Iglisi Watch · Durrës, Albania · June 2026.