Watch Spring Bar Sizes + How to Measure a Band for Replacement

A spring bar is the small spring-loaded steel pin that holds your watch band to the case: one bar between each pair of lugs, two per watch. When a band wears out or you want a new one, the single question is "what size replacement do I need?", and the answer is two numbers, not one: the width between your lugs (which is both the band width and the spring bar length) and the length around your wrist the band must wrap. This page covers measuring both, plus the pin sizes themselves. If instead you want to shorten the band you already have, that is a different job: see how to adjust a watch band.

Quick reference: standard widths and the bars they take

Most traditional watches use even-numbered lug widths in 2mm steps, and replacement bars are sold in the same numbers, in 1mm steps across the odd sizes too. Find your width, buy that bar:

Odd widths (19mm, 21mm) exist mostly on luxury and vintage watches; bars are made in those sizes but selection is thinner. For what width a specific model takes, don't guess: look it up in the lug width chart by brand and model or the watch database, both of which list confirmed widths for popular watches.

Spring bar diameters: 1.5, 1.8, and 2.0mm

Length is half the spec. The other half is the bar's diameter, its thickness, which must fit the holes drilled in your lugs. The industry standard sizes:

Thicker bars are stiffer and stronger, but the diameter is set by your watch's lug holes, not by preference: a bar too thin rattles and works the holes oval, a bar too thick will not seat. When in doubt, match the diameter of the bar that came out. If the bar is lost, 1.8mm fits most watches; err smaller, not larger.

The Seiko exception. Seiko divers use oversized "fat" bars, 2.5mm thick with 1.1mm tips, sold under Seiko part number C220FS for 22mm models like the SKX007, SKX009, SKX173, and the Turtle SRP777 (and 20mm versions for other Prospex divers). This is confirmed by multiple independent OEM parts listings rather than a published Seiko spec sheet, so verify the part number when ordering: a standard 1.8mm bar will feel loose in a Seiko diver's lug holes, and the correct fat bars are cheap and widely stocked. Seiko-specific lug widths per model are in the watch database.

How to measure the width (the number the band and bar share)

The width is the clear gap between the inside faces of one pair of lugs, in millimeters, and it is the same number you shop with for both the band and the bars:

1. Check for a stamp first. Many bands have the width printed on the underside near the spring bar, and case backs sometimes carry it too. A stamp beats a measurement.
2. Ruler method, no tools. Lay a metric ruler across the lug gap, looking straight down at the watch with the ruler resting where the spring bar passes. Read inside edge to inside edge. Never measure from the outside of the lugs: that reads several millimeters too big.
3. Calipers for odd sizes. If the ruler says "about 19 or 20", calipers against the inner lug faces settle it. Between sizes, round down: manufacturers build cases on whole millimeters, and a 19.3mm reading means 19mm lugs.
4. Measure the watch, not the strap. Leather shrinks and straps compress; a 20mm strap worn for years may measure 19.5mm. The watch head is the truth.

How to measure pin size when the bar is still installed

You rarely need to remove a spring bar to size its replacement, because the installed bar encodes its own length:

• Length: measure the internal lug gap as above. The bar inside spans it exactly, so the gap is the bar's tip-to-tip length. 20mm gap, 20mm bar.
• Diameter: if you cannot slide calipers over the bar's middle through the strap, work from the lug holes: bars are sized to fill them, and a quick-release bar that feels loose in the hole means you can go up to the next standard diameter (1.5 to 1.8mm, 1.8 to 2.0mm).
• If the bar is already out: lay it on a millimeter ruler, tip to tip, for length; hold it against a known bar or a drill bit shank of stated size to compare diameters. Take the old bar to any watch shop or parts counter and they will match it in seconds.
• Quick-release check: a small lever on the side of the bar means quick-release. Compress it with a fingernail to slide the strap out with no tool; replacement quick-release bars are sold in the same length and diameter numbers.

Measuring a band for replacement: the length question

Width decides whether the band attaches; length decides whether it wraps your wrist. Two-piece band lengths are written as two numbers, like 115/75mm: the long side with the holes (115) and the short buckle side (75), neither counting the buckle itself. To get your numbers:

1. Best case, measure a band that already fits: measure each piece end to end, excluding the buckle, and order the same pair of numbers. This transfers your fit exactly, buckle position and all.
2. No reference band: measure your wrist circumference where the watch sits (the wrist measuring guide covers this in 60 seconds with a strip of paper), then choose by size class: roughly 105/70 to 110/70mm for wrists under 16.3cm, 115/75 to 120/75mm for average wrists, 125/80mm and up above 18cm. The strap must also span the watch case and pass the buckle, which is why you need around 30-60mm more strap than bare wrist circumference.

The full wrist-size-to-strap-length mapping is its own table: see the strap length chart by wrist size, or the NATO strap length guide for one-piece nylon bands, which size differently (a single length, regular vs long).

What to actually order

• Replacement strap: width first (lug width, exact), then length (two numbers), then taper if you care how the band narrows toward the buckle.
• Replacement spring bars: length equals lug width, diameter matched to the old bar or 1.8mm default, in pairs. They cost a dollar or two and are sold by size; most new straps ship with bars included, so order spares for the drawer, not the install.
• Tool: a forked spring bar tool costs a couple of dollars and releases standard bars; quick-release bars need nothing but a fingernail. The full removal and refit walkthrough, with the tape-the-lugs trick, is in the spring bar section of the band adjustment guide.
• Smartwatch owners: Apple, Galaxy, and Fitbit bands use proprietary connectors or built-in pins, not generic spring bars; see the smartwatch sizing guide for those systems.

Related guides

The band size chart lists confirmed lug widths by watch model, the strap length chart maps wrist size to band length, and the adjustment guide covers shortening a band you already own: links, clasp, or leather holes. To understand why the watch head itself fits or doesn't, the lug-to-lug explainer and the wrist size calculator are the tools.

Sources

• Spring bar anatomy, two-measurement sizing (length equals lug width, diameter matched to lug holes), and quick-release mechanism: cnswatchbands.com complete spring bar guide, soflypart.com watch band pins replacement guide, and smartlet.io collector's guide, three independent references in agreement.
• Common diameters 1.5 to 2.0mm and their use classes (1.5mm dress, 1.8mm standard for most watches, 2.0mm heavy duty): smartlet.io specification table, gemsmakers.com thickness chart, and thewatchrabbithole.com diameter explainer.
• Seiko fat bars 2.5mm with 1.1mm tips, part C220FS, 22mm for SKX007/SKX009/SKX173/Turtle SRP777 and 20mm for other Prospex divers: Long Island Watch (authorized Seiko dealer, "22mm wide and 2.5mm thick"), cpsathailand.com genuine Seiko packaging listing (thickness 2.5mm, model fit list), and masar-shop.com compatibility table (2.5mm body, 1.1mm tip). OEM parts listings, not a Seiko-published document.
• Width measuring method (ruler inside-edge to inside-edge, never outside the lugs, width stamped on strap underside, round down between sizes): watchband.direct mm size guide, catalystcase.com measuring guide, watchpartsfit.com lug width guide, wizeband.com strap replacement guide.
• Installed-bar sizing (internal lug width equals required bar length, measure the watch head not the strap): gemsmakers.com sizer guide and the Quora watch band pin measuring thread.
• Band length notation (long/short excluding buckle) and wrist-plus-30-60mm allowance: helvetus.com strap length guide, garminwatch.blog length guide, straphome.com size guideline, alligatorwatchstrap.com measuring guide.